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Weather and Climate of the Reno-Carson City-Lake Tahoe Region Nevada Bureau of Mines and Geology Special Publication 34 Photo by Mark Vollmer Photo by Jack Hursh Pyramid Lake as seen from Thunderbolt Bay with the snow-covered Pah Rah Range and mountain lee wave clouds in the distance. Truckee Meadows Remembered historical ranch outbuilding display at Bartley Ranch Park, Reno, late December 2004. Cover photo: Mountain lee wave (lenticular) clouds, with rotor clouds beneath, seen at sunset from U.S. Highway 395 south in Reno. Photo by Kris Ann Pizarro. Nevada Bureau of Mines and Geology Special Publication 34 Weather and Climate of the Reno-Carson City-Lake Tahoe Region Brian F. O’Hara Meteorologist National Weather Service, Reno, Nevada Gary E. Barbato Senior Service Hydrologist National Weather Service, Reno, Nevada John W. James Former Nevada State Climatologist and Professor Emeritus Department of Geography University of Nevada, Reno Heather A. Angeloff Research Assistant, Nevada State Climate Office Climatologist/Staff Scientist, Western Regional Climate Center Tom Cylke Senior Meteorologist National Weather Service, Reno, Nevada 2007 In memory of John W. James 1933–2007 University of Nevada, Reno College of Science Mackay School of Earth Sciences and Engineering Contents Overview Introduction Convective Weather 48 Thunderstorms 48 Thunderstorm wind gusts Dry microbursts 49 Hail 50 Tornadoes 50 Funnel clouds 51 Dust devils 51 Lightning 51 3 5 Temperature 7 Historic heat waves 13 Historic cold periods 16 Degree days 18 Temperature inversions and air pollution Growing season and frost 21 19 Wildfires Precipitation 23 Rain 23 Snow 25 Lake effect snow 27 Historic snowstorms 28 Snow cover 31 Historic winters 32 Ice storms 35 Humidity 36 Fog 36 Freezing fog (pogonip, rime) Drought and Evaporation Drought 39 Evaporation 40 49 52 Floods 54 River floods 55 Largest historical floods in western Nevada and the eastern Sierra Nevada 56 Flash floods 64 Flood frequency in the Truckee, Carson, and Walker river basins 67 The top 25 weather-related events in the region since 1850 68 38 Acknowledgments 39 References Glossary Wind 42 Washoe Zephyr 42 Mountain lee waves 46 Synoptic-scale wind events 47 Dust storms and sandstorms 47 72 74 77 Appendix A. Weather station history Reno 81 Carson City 82 Tahoe City 82 81 Dedicated to the employees (past and present) of the National Weather Service (NWS) Forecast Office in Reno, Nevada, and to the employees of the NWS (and before that the U.S. Weather Bureau) nationwide. Their selfless service has benefited the American public for well over a century. Without the data that they collected and archived, the writing of this publication would not have been possible. 2 Overview by John W. James There is great diversity in the Reno-Carson City-Lake Tahoe region’s climate due to large differences in elevation, topography, and the proximity of the region to the eastern Pacific storm track (terms in bold text are defined in the glossary). The location of the jet stream over northern California and Nevada during the winter causes a mid-winter precipitation maximum over the region. There are actually two sources of moisture during the warmer half of the year (which is generally the drier season) and one source during the colder half of the year (the wet season in most of Nevada). The sources during the warmer part of the year (June through September) are the Gulf of California (and the adjacent eastern Pacific Ocean west of Baja California) and the Gulf of Mexico. The eastern Pacific is the primary breeding ground for rain and snowstorms that affect the state during the colder half of the year. Also, drying westerly flow down the eastern slopes of the nearby Sierra Nevada tends to add to summer stability and dryness. In general, precipitation ranges from as low as 5 inches in the valleys to as much as 50 inches along the upper parts of the Carson Range and the Lake Tahoe basin, the wettest area of Nevada. For example, the greatest water year precipitation total, 96.91 inches, fell at Tahoe Meadows, near Mt. Rose, in 1982–83, at the 8500foot elevation. As much as 37 inches of precipitation (rain plus water equivalent in snow) has fallen in one month at Tahoe Meadows in both January 1969 and February 1986, with a record one-month snowfall of 199 inches in January 1916 at Marlette Lake, just three miles south of Tahoe Meadows. Climate has an obvious influence on settlement patterns, such as settlement for industry, ranching, tourism, vacationing, and retirement. Precipitation amounts and distribution, both seasonally and annually, are important for water needs, but are a special concern for certain settlement patterns (e.g., irrigated farming and waterrelated industry, and water use for domestic and recreational purposes). Sunshine is not only an important factor for health, but it also lends promise as an alternative energy source. The region ranges from 60 to 70% of the possible sunshine hours in winter and 80 to 85% in summer. Wind can be welcome on a hot day, but it can create dangerous conditions during a mid-winter cold spell. Each of these factors is an important part of the area’s climate. About two-thirds of the average annual precipitation of the region occurs from November through March, with the three summer months (June, July, and August) contributing less than 10% of the annual total. Average annual snowfall is light in the valleys of western Nevada (25–45 inches), but up to 350 inches is common in the higher elevations of the Sierra Nevada and the Carson Range. This is normally the snowiest area of Nevada, and the 15 to 20 ski areas in and adjacent to the Lake Tahoe basin are evidence of that. The heavier snowfall of the Sierra Nevada can make travel in the mountainous area between Lake Tahoe and the cities of Reno and Carson City difficult in wintertime, although road crews try to keep main highways clear as much as possible. Water deficits are common, especially in the more arid areas. For example, average annual precipitation is about 7½ inches in Reno, about 10 inches in Carson City, and about 20 inches at Glenbrook in the Lake Tahoe basin. Valleys average 40 to 50 days of measurable precipitation per year, whereas the Carson Range averages up to 80 days per year. The Reno-Carson City area also has the mildest wintertime temperatures in the northern half of Nevada. These milder temperatures are due to a prevailing westerly airflow and the distance from the colder air masses that invade Nevada from the northeast. Temperature inversions are prevalent much of the year due to optimum nighttime cooling conditions and topography, wherein cold air drains down to valley floors on most clear, calm nights. This is a problem at times of high pressure stagnation, especially during winter in urban areas, as air pollutants are trapped by the cooler valley floor temperatures. The low sun angle and lack of storminess allow for little heating and/or wind to break the inversion. Extremes of cold or heat are not as prevalent here as they are in other parts of Nevada. Winter nights rarely fall below zero, and days are usually above freezing, except in the mountains. Summer days are warm, but nights pleasantly cool, with just a few days near 100ºF likely every year in the valleys (Reno’s all-time high of 108°F occurred in July 2002). Around Lake Tahoe, summertime highs are usually in the 70s and 80s in most areas and evening lows are generally in the 30s and 40s. The frostfree season lasts about 120–130 days in the valleys, but only 80–95 days or less in the Lake Tahoe basin, where late spring and early fall frosts are common. Occasionally during the winter season, strong downslope winds may reach destructive levels. This was the case for example, in November 1981, when an unusually high 101 mph (miles per hour) wind gust was recorded in southwest Reno. This was associated with a powerful winter storm from off the Pacific that caused significant damage in the Reno area. Air conditioning can be an important comfort factor during summer days in the valleys of western Nevada as temperatures frequently rise to 90°F or higher. It is not needed as much at Lake Tahoe, however, because days over 90°F are infrequent. Wintertime heating requirements are more important, with the abundance of sunshine allowing for solar devices to be more useful in this region. Heating requirements are stringent in the Lake Tahoe basin, not due to extreme cold, but rather because of a combination of precipitation, wind, and cloud cover during storms. 3 Photo by Mark Vollmer Thunderheads build over Lake Tahoe's south shore, as seen from Tahoe Rim Trail near Spooner Summit. In a Nutshell • Sunshine is abundant throughout the year: 60–70% of possible sunshine in winter and 80–85% of possible in summer. • The Reno-Carson City-Lake Tahoe region is the only one in Nevada with a pronounced wintertime precipitation maximum (two-thirds falls from November through March). • Frost-free season is 120–130 days in the valleys, but only 80–95 days or less in the Lake Tahoe basin. • Annual precipitation averages 5–12 inches in valleys and 40–50 inches in the Carson Range on the east side of the Lake Tahoe basin. • Strong winds of 70 mph or more associated with winter storms occur every winter. • Annual snowfall averages 25–45 inches in valleys and up to 350 inches in the Carson Range (the snowiest area of Nevada). It should be noted that the Reno weather observation site has been staffed by U.S. Weather Bureau (USWB) and later National Weather Service (NWS) staff from its inception in November 1905. Thus a fairly complete record of weather and climate data is available for Reno for the past 100 years. The weather observation sites at Carson City and Tahoe City have not been staffed by USWB and NWS employees, but by volunteer cooperative weather observers. The data that they collected (although just as valuable) was generally restricted to temperature, precipitation, and snowfall. This should be kept in mind when studying the data in the following document. Data for wind speed and direction, relative humidity, occurrences of fog, and occurrences of thunderstorms have not been collected at Carson City and at Tahoe City, so the figures for these data below will only reflect data that has been collected at Reno. Figures for temperature, precipitation, and snowfall, however, will reflect data from all three sites. Changes in the location of weather observation sites over the years at Reno, Carson City, and Tahoe City are described in Appendix A. • Snow normally covers the ground above 7000 feet in the Carson Range from about November to April and does cause some travel impedances during storm periods. • Because of the relatively dry summers there are typically only 40–50 days per year with precipitation in the valleys, 70–80 days in the mountains. • The region has fewer temperature extremes than are found in the remainder of Nevada. • Air conditioning is not necessary but does add to midsummer comfort. Winter heating is necessary, but abundant sunshine makes possible solar heating devices. • Winter nighttime temperature inversions are a problem concerning air pollution in urban areas, especially along valley floors. 4 Photo by Chris Ross The Stone Mother or Squaw and Basket formation, Pyramid Lake. This photo, taken in the early 1980s, shows the tufa formation surrounded by water just south of the Pyramid on the east side of Pyramid Lake . Introduction by Brian F. O’Hara and Heather Angeloff east” (Smith, 2000). The lake formed after lava from Mt. Pluto dammed the north end of the basin approximately 2 million years ago. Numerous other geologic faults are located throughout western Nevada and the eastern Sierra, and close to 30 earthquakes of magnitude 4.0 or greater on the Richter Scale have been reported in the area within the last 150 years. The number and strength of earthquakes generally decreases as you move east from the Sierra Nevada, with the vast majority of Nevada earthquakes being recorded in the western half of the state. Sagebrush is the dominant plant in the dry valleys of the western Great Basin. However, as you climb the Carson Range the vegetation changes to a more alpine type. The first trees encountered are Jeffrey pine, interspersed with montane chaparral; and higher up in elevation you find white fir. On the other side of the Carson crest, on the eastern side of Lake Tahoe, you also find mainly Jeffrey pine and white fir. On the more thickly forested west side of Lake Tahoe, the trees include Jeffrey, sugar, and ponderosa pines; white fir; and incense cedar at lower elevations. Higher up are found Jeffrey, lodgepole, and western white pines; Sierra juniper; and red fir (Howald, 2000). The Truckee River begins at Tahoe City and winds its way between the Carson Range and Peavine Mountain, flows east through the valley known as Truckee Meadows, and then empties into Pyramid Lake northeast of Reno. Between the Carson Range to the west and the smaller mountains to the east a valley extends from the Truckee Meadows south through Carson City to Minden and Gardnerville. This valley, with Reno as its hub, has the largest population density in Nevada outside of Las Vegas. Even though they are close to one another geographically, the climate of the Reno and Carson City area is quite different than the climate of the Lake Tahoe basin. Reno and Carson City are located at the base of the eastern slopes of the Sierra Nevada in the western part of the physiographic region known as the Great Basin. The Great Basin extends from the crest of the Sierra Nevada east to the Wasatch Front in central Utah (Figure 1). It is a closed basin because no rivers or streams flow out of it. Most surface water is lost through evaporation. The Great Basin is a high desert with an average elevation of 5000 feet above sea level. By contrast, the Lake Tahoe basin is an alpine basin with Tahoe City receiving ten times the snowfall that Reno and Carson City receive. The Lake Tahoe basin is cooler because it is at a higher elevation and it has more precipitation and higher humidity than do the valleys just east of the Sierra Nevada. Actually, the mountains immediately west of Reno and Carson City belong to the Carson Range, a spur of the Sierra Nevada. To the southwest of Reno, Slide Mountain (9694 feet in elevation) and Mount Rose (10,776 feet) are part of the Carson Range. Just to the northwest of Reno is Peavine Peak (8260 feet), and southeast of Reno are the Virginia Mountains with peaks over 7000 feet. South of the Virginia Mountains, east of Carson City, are the Pine Nut Mountains with peaks rising to over 9000 feet. The Pah Rah Range extends to the northeast of Reno with elevations over 8000 feet. Lake Tahoe lies in a basin that formed when it “dropped down along faults on either side, while the Sierra block rose on the west and the Carson Range on the 5 Figure 1. Western Nevada and northeastern California, showing some of the locations mentioned in this publication. Inset shows map location in relation to the Great Basin. 6 Photo by Chris Ross Photo taken in alfalfa field on the Pyramid Lake highway. The air temperature was high enough to allow irrigation spraying from the wheel lines, while the surface temperature was low enough to freeze the water when it hit. Temperature by Brian F. O’Hara The Reno-Carson City-Lake Tahoe region experiences a wide range of temperatures on both a daily and a yearly scale. This is mainly due to the relatively high elevation of the Great Basin and to the relatively dry air mass typically over the region throughout most of the year. The Great Basin has elevations ranging from around 4000 feet in the valleys to over 10,000 feet in the highest mountain ranges. Because of these high elevations, incoming solar radiation over the region is more intense and the air mass near the ground is less dense than they are at lower elevations. Thus, there are fewer molecules in the air mass to absorb or reflect the sunshine passing through. The air also tends to be quite dry over the region. This means that there is less water vapor in the air to absorb energy before it reaches the surface. Temperatures during the summer months at Reno and Carson City often reach the 90s during the afternoon and can even rise to over 100ºF (temperatures are in degrees Fahrenheit [ºF] throughout this publication). Temperatures of at least 100º can be expected at least once each summer and up to five times or more every other summer, on average. Because of its higher elevation (and proximity to a large body of relatively cold water), temperatures at Tahoe City, on the northwest shore of Lake Tahoe, tend to be cooler than at either Reno or Carson City; afternoon highs at Tahoe City tend to be 10 to 15° cooler during the summer. The average high temperatures that can be expected during July across the eastern Sierra and western Nevada are shown in Figure 2 on page 9. The dry atmosphere over the western Nevada valleys heats up quickly during the day because there is less water vapor in the air mass to absorb the solar energy passing through. At night, however, the ground and the air immediately above it cool rapidly due to the lack of cloud cover. Heat is radiated very efficiently and the air near the ground can cool 40° below its afternoon peak. After highs in the mid 90s, the temperature can drop into the mid 50s by sunrise. This large temperature range can make the hot conditions during the afternoon more bearable. Occasionally a light jacket may be needed in the evening even during mid summer. These temperature ranges are also experienced at Tahoe City. The average low temperatures that can be expected during July across the eastern Sierra and western Nevada are shown in Figure 2 on page 9. A large daily temperature range is also noticeable during the winter but it is usually not as large as that experienced during the summer. This is because the relative humidity of the air mass tends to be higher during the winter. As in the summer, the dew point temperature near the ground may be in the 20s. However, unlike the 90º temperatures seen during the summer in Reno or Carson City, afternoon temperatures (even at Tahoe City) during the winter are closer to the dew point readings. Solar radiation is absorbed by water vapor in the atmosphere. Thus, solar energy that is absorbed cannot reach the ground. Cloud cover is also more common during the winter as a result of large synoptic-scale storms passing through the region. This cloud cover tends to keep daytime 7 temperatures at Carson City are similar to those at Reno but temperatures at Tahoe City (on the west shore of Lake Tahoe) tend to be 10 to 15° cooler. Western Nevada skies are relatively clear most of the year. With the dry atmosphere over the region there simply is not enough water vapor in the air mass that can condense into clouds. Reno receives almost 80 percent of the solar energy that enters the atmosphere (Figure 4). This means that an average of around 20 percent of the sun’s energy is absorbed or reflected by molecules in the atmosphere. Sunshine data are not available for Carson City or Tahoe City. Figure 5 shows the various sky conditions reported over Reno throughout the year. It is apparent that days tend to be sunnier and nights clearer at Reno during the summer than at any other time of year. This contributes to the larger daily temperature ranges during the summer than during the winter. During July, August, and September, skies are clear two-thirds of the time, and days are cloudy (nearly complete cloud cover) only two or three times per month. During the winter, skies are cloudy about half the time and skies are clear almost a third of the time. Higher relative humidity and more frequent synoptic-scale storms passing through the region contribute to the greater cloud cover during winter. temperatures from rising as high as they would otherwise, and it keeps nighttime temperatures warmer because radiation is not lost to the upper atmosphere as easily as it would be under clear skies. Afternoon high temperatures during the winter may be in the 30s or 40s, both in the western Nevada valleys and at Lake Tahoe. In the absence of winter storms, skies tend to be relatively clear during the winter, so afternoon temperatures can rise fairly quickly and the air mass can then cool considerably at night. Daily temperature ranges during the winter can be 30° or even 40° because winter afternoon highs reach the 40s or 50s and then cool down into the teens or 20s at night at Reno and Carson City (Figure 2 on page 9). It is rare for temperatures to fall below zero at night during the winter in either western Nevada or at Lake Tahoe. Even with its higher elevation, the water in Lake Tahoe helps to modify the air mass and keeps temperatures from reaching the all-time monthly record lows seen at Reno and Carson City (Figure 2 on page 9). Table 1 and Figure 3 show normal high and low temperatures and record high and low temperatures for each month at Reno, Carson City, and Tahoe City. Table 1 also lists the years in which the record highs and lows occurred. Monthly Table 1. Monthly temperatures (ºF) at Reno and Carson City, Nevada, and Tahoe City, California Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec Record high (year)* Reno 71 (2003) 76 (1888) 83 (1966) 89 (1981) 98 (1910) 104 (1940) 108 (2002) 105 (1983) 101 (1950) 91 (1980) 77 (1980) 71 (1940) Carson City 72 (2003) 76 (1972) 81 (1966) 88 (1981) 93 (2003) 101 (1950) 105 (2002) 103 (1972) 103 (1950) 91 (1964) 78 (1960) 75 (1958) Tahoe City 59 (1990) 60 (1985) 67 (1996) 74 (1981) 81 (1986) 90 (1961) 93 (1934) 94 (1933) 87 (1955) 80 (1933) 70 (1988) 60 (1990) Normal high (1971–2000) Reno 45.5 51.7 57.2 64.1 72.6 82.8 91.2 89.9 81.7 69.9 55.3 46.4 Carson City 45.6 50.7 56.6 63.2 71.6 81.2 89.2 87.8 80.2 68.8 54.7 46.2 Tahoe City 40.5 42.0 45.1 51.4 60.1 69.2 77.5 77.0 70.1 60.0 47.9 41.4 Normal low (1971–2000) Reno 21.8 25.4 29.3 33.2 40.2 46.5 51.4 49.9 43.1 34.0 26.4 20.7 Carson City 21.7 25.4 29.5 33.0 39.7 46.1 50.7 49.1 42.4 33.4 26.4 20.8 Tahoe City 20.1 21.3 24.3 27.7 33.5 39.6 44.7 44.8 39.6 32.3 25.5 20.6 Record low (year)* Reno -19 (1890) -16 (1989) -3 (1897) 13 (1956) 16 (1896) 25 (1954) 33 (1976) 24 (1962) 20 (1965) 8 (1971) 1 (1958) -16 (1972) Carson City -20 (1949) -22 (1989) -5 (1952) 12 (1972) 18 (1967) 27 (1954) 33 (1987) 26 (1968) 20 (1965) 6 (1971) -4 (1994) -19 (1990) Tahoe City -15 (1916) -15 (1989) -6 (1935) 5 (1999) 9 (1974) 24 (2005) 22 (1975) 29 (1957) 21 (1965) 9 (1971) 1 (1931) -16 (1972) * Since 1888 at Reno, 1948 at Carson City, and 1914 at Tahoe City. 8 Figure 2. Average high and low temperatures for January and July across the eastern Sierra and western Nevada. Copyright © 2005, PRISM Group, Oregon State University, www.prismclimate.org. Maps created November 1, 2005. 9 Photo by Mark Vollmer Figure 13. Average annual precipitation and snowfall across the eastern Sierra and western Nevada. Precipitation map copyright © 2005, PRISM Group, Oregon State University. Snowfall map created by Gary Johnson. Evening thunderstorm over distant Pine Nut Mountains. View across Washoe Valley and the Virginia Range from the Mt. Rose Highway. Lights of Washoe City can be seen in the near distance. 10 Photo by John James Photos by Kris Ann Pizarro Flow control structure at the outlet of Lake Tahoe into the Truckee River. The lake level occasionally drops below the outlet during droughts such as the one in 1991 when this photo was taken. See figure 20 on page 39. Comparison, Washoe Lake, August 2004 (dry) and June 2006 (full). 11 Photo by Mark Vollmer Photo by Mark Vollmer Cirrus clouds over the Truckee Meadows. Smoke from the Martis Creek wildfire over the Carson Range between Reno and Lake Tahoe, June 2001. Downtown Reno is in the foreground. 12 Figure 4. Percent of solar radiation entering the atmosphere that reaches the surface at Reno, Nevada (1961–2005). The annual average is 79 percent. High pressure forms over the Great Basin during the winter. Extensive snow cover cools the lower atmosphere and helps to strengthen this area of high pressure (Hill, 1993). The downward motion associated with this high pressure can keep pollutants trapped near the surface for days at a time. The air over western Nevada is cleaner than it has been in decades past (in part due to a ban on wood burning, and annual smog checks being required on automobiles), but temperature inversions can still keep hazy conditions across the region during the winter, especially in urban areas. HISTORIC HEAT WAVES Warm temperatures can be expected each summer in the valleys of western Nevada. Readings of at least 100º can also be expected just about every summer, usually in July or August. However, some warm periods stand out as particularly severe. Some of the most impressive heat waves of the last 100 years in the Reno and Carson City areas are listed below. The Lake Tahoe basin does not usually experience temperatures as high as those recorded in the valleys east of the Sierra. Figure 3. Monthly temperatures (ºF) at Reno and Carson City. Nevada, and Tahoe City, California. 13 July 1931. This is the sixth warmest July on record at Reno with a monthly average of 77.4ºF. Eight days in the last half of the month recorded daily high temperatures of at least 100º. For six consecutive days (the 18th through the 23rd) the high temperature was 102º or greater. On the 19th the high temperature was 105º and on the 20th it reached 106º. This reading was the all-time record high for Reno until July 2002 when readings on two days reached 108º. Up at Lake Tahoe it was also warm; the temperature at Tahoe City reached at least 90º from July 20 through the 23rd. The 93º reported on the 20th remains the all-time record high for the month of July at Tahoe City. August 1933. For five consecutive days (11th through the 15th) the daily high temperature at Reno was at least 100º. The high temperature of 103º on the 13th is still the record high for that date. At Tahoe City the afternoon temperature was over 90º for four consecutive days from the 12th through the 15th. The 94º recorded on the 15th remains the highest temperature ever recorded at Tahoe City. July 1959. This was a very warm July with temperatures reaching 100º on seven days in Reno. On six consecutive days (16th through the 21st) the high was at least 100º. On July 20 the temperature reached 100º at Carson City, still the record high for that date. It got up to 101º on the 11th and this remained the record high for that date at Carson City until the incredible summer of 2002. Temperatures dropped into the 50s at night, making the heat more bearable. At Tahoe City afternoon highs during this period were around 10° cooler than those experienced at Reno and Carson City. The weather map for July 18, 1959 is shown in Figure 6 . July 1980. Warm weather visited the region in late July with temperatures reaching at least 100º on seven consecutive days (21st through the 27th) at Reno. The readings on the 25th, 26th, and 27th (104º, 104º, and 103º, respectively) are still the all-time record highs (or tied for the record high) for these dates. At Carson City the temperature reached 100º on the 22nd and 101º on the 27th. The weather map for July 26 (Figure 6) shows the ridge of high pressure that was over much of the Intermountain West. July 2002. This is the fourth warmest July on record, and the third warmest month ever at Reno. It had been the warmest ever until July 2003 broke the record. Temperatures reached at least 100º on six days. On four consecutive days (9th through the 12th) the high was at least 101°, and reached 108º on both July 10 and 11, setting new all-time high temperature records for Reno. Not only was it hot during the day, but it remained warm at night. From the 10th through the 17th, the temperature never dropped below 61º. On the morning of the 12th, after the second day of 108º temperatures, the low was a balmy 74º. The record warmth during this month at Reno can mainly be attributed to the abnormally warm minimum temperatures at night. This warmth is the result of the urban heat island effect. At Carson City new record highs were set on four days with readings of 100º, 105º, 104º, and 99º on the 9th, 10th, 11th, and 12th, respectively. The 105º reading on the 10th is now the highest temperature ever recorded at Carson City. Figure 6 shows the surface weather map for July 11, 2002. Figure 5. Average number of cloudy, partly cloudy, and cleardays at Reno, Nevada (1943–2004). 14 July 2005. With an average temperature of 80.0° this is the warmest month on record at Reno. The high temperature for each day from the 12th through the 21st Figure 6. Surface weather maps for July 18, 1959, 1:00 am EST; July 26, 1980, 7:00 am EST; July 11, 2002, 7:00 am EST; and January 8, 1890, 8:00 am EST (pressure in millibars reduced to sea level). Maps courtesy of the NOAA Central Library Data Imaging Project. 15 the 11th and down to -9º on the 12th. After a powerful storm dropped over 2 feet of snow on Reno (22.5 inches on the 17th alone) temperatures plummeted. On the morning of the 20th the recorded low was -11º and on the 21st the temperature dropped to -17º. After a third snowstorm moved through the region late in the month, the temperature dropped to -13º on the 31st. This remains the fifth coldest January on record at Reno. It was a snowy month at Lake Tahoe with 238 inches of snow being reported at Tahoe City. Ten feet of snow was on the ground by the end of the month. The temperature dropped to below zero on six days. On the 11th the morning low at Tahoe City was -14º. The temperature dropped to -15º on the 30th, and -14º was reported on the 31st. exceeded 100º, setting a new consecutive-day record of 10 straight days at or above 100º. The temperature rose to 104º on both the 12th and the 16th. It was warm throughout the region. Carson City reported highs in the upper 90s during this same 10-day period. The temperature there on the 17th reached 100º. At Tahoe City the afternoon highs were 80º or above from the 11th through the 20th. HISTORIC COLD PERIODS During the winter temperatures can plummet after the passage of a strong cold front. Temperatures can drop to below zero at night with readings 20° to 30° below normal. The cold air mass can remain over the region for a week or longer. This can be a serious threat to public safety as public utilities have a difficult time supplying enough power for heating. The very cold weather can also cause pipes to freeze, making life even more difficult. Snow cover can remain for weeks because the cold air mass does not allow for rapid melting. Even though cold weather can be expected every winter in the region, some cold outbreaks can cause incredible hardship and are remembered for years to come. Some memorable cold outbreaks are listed below. January 1937. This was an extremely cold month with the average temperature on every day except one (January 14th) below normal at Reno. The average temperature for the month was 15.8º. The morning low temperature was below zero on seven consecutive days (January 7 through 13). The low was -10º on the 7th, -16º on the 8th, and -14º on the 9th. It remained cold throughout the rest of the month with the morning low on the 20th reaching -12º, and then -14º on the 21st. This is the second coldest January on record at Reno. It was also bitterly cold at Lake Tahoe with record low temperatures being set at Tahoe City. On both the 9th and 21st the temperature dropped to -14º. The temperature dropped to -13º at Tahoe City on the 20th. At Boca (5 miles northeast of Truckee), the temperature fell to -45° on January 20th. This remains the all-time record low temperature for the state of California. January 1890. Cold conditions first hit the region in late December 1889 when the temperature at Carson City dropped to -7º on the 29th. The cold weather continued through January. A bitterly cold air mass moved into the region early in the month with temperatures dropping to well below zero at Carson City on four consecutive nights. On January 6 the low temperature was -10º. The next morning the low was -17º, and on both the 8th and the 9th the morning low was an incredible -22°. There was another report from Carson City of the temperature dropping to -27º the morning of the 8th. (However, these readings are not listed in the records because official readings at Carson City only date from 1948.) At Reno the morning low on both the 7th and the 9th was -18º. The lowest temperature for the entire month at Reno occurred on January 8 when the temperature dropped to 19º below zero. This reading remains the all-time record low for Reno for any month. The strong dome of high pressure over the Intermountain West on January 8, which helped temperatures drop to record lows, can be seen on the weather map for January 8, 1890 in Figure 6. Cold weather was experienced later in the month when the temperature at Carson City dropped to -4º on the 22nd. Even colder conditions occurred the last week of January 1890 as temperatures at Carson City dropped to -11° on the 27th and -9° on the 28th. January 1949. A very cold month with an average temperature of 14.1º reported at Reno. Only three days during the month had an average temperature greater than 20º. Each day during the month the average temperature was below normal. The morning low temperature was below zero on all but eight days. The morning low was -10º on the 11th and -11º on the 12th. The temperature fell to -12º on January 15. Bitterly cold weather continued through the rest of the month with lows of -16º on the 25th and -15º on the 26th. Incredibly, the average minimum temperature for the month was 2.2°! This is still the coldest January on record at Reno. At Carson City the morning temperature dropped to -15º on the 4th, -10º on the 17th, -16º on the 25th, and -20º on the 26th. The -20º reported on the 26th remains the record low temperature for January at Carson City. Figure 7 shows the ridge of high pressure that was over much of the western United States on January 25. Conditions were not as bitterly cold at Lake Tahoe during the month. However, the temperature dropped below zero on five mornings at Tahoe City. The lowest reading for the month was -6º reported on the 4th. January 1916. The snowiest month on record at Reno helped keep average temperatures low. Over a foot of snow fell at Reno on January 9 and 10. After this storm system moved through, temperatures dropped to -1º on 16 First half of December 1972. Incredibly cold temperatures were recorded during the first half of December. This remains the second coldest December on record at Reno. Low temperatures on six of the days are still the all-time record lows for those dates. The morning low at Reno dropped to -12º on the 5th. After a slight warmup temperatures plummeted. During the second week of December daily average temperatures were over 20° below normal. From the 9th through the 11th average temperatures were over 30° below normal. On the 8th the morning low fell to -12º. Low temperatures on the 9th, 10th, and 11th were -16º, -11º, and -15º, respectively. The -16º on December 9 remains the record low temperature for the month in Reno. The high temperature on the 9th was only 6˚ above zero. This remains the lowest maximum temperature ever recorded at the Reno airport. The cold front that moved through the Sierra and western Nevada on January 9 ushered in the incredibly cold air mass (Figure 7). During the first half of December at Carson City, the temperature dropped to below zero on six days. These six readings remain the lowest ever recorded on these dates. It dropped to -11º on the 5th. As at Reno, there were a few days of warmer temperatures before the cold set in again. On the morning of the 9th the temperature dropped to -14º, and two days later, on the 11th, the morning low was -18º. Up at Lake Tahoe it was also bitterly cold. For four mornings, from the 9th through the 12th, record low temperature readings were set. On the 9th Tahoe City reported a low of -10º. On the 10th the low was -11º, and on the 11th the morning low was -16º. On the 12th the low was still below zero at -4º. The low temperatures for these four days remain the record lows for these dates at Tahoe City. In fact, the -16º reported on the 11th is the lowest temperature ever recorded at Tahoe City. Early February 1989. An incredible cold outbreak in early February saw daily average temperatures drop to almost 40° below normal. In Reno, on the 6th and 7th, the average temperature was 37° colder than it usually is during the first week of February. The temperature on the morning of the 5th fell to -10º. On the 6th the morning low was -15º, while on the 7th the low fell to -16°. This is the all-time record low temperature for February at Reno. It was still bitterly cold on the 8th with a low of -12º. At Carson City the temperature dropped to -19º on the 6th, -22º on the 7th, and -17º on the 8th. The -22º on the 7th is the lowest temperature ever recorded at Carson City (using official weather data from July 1, 1948 to present). It was also incredibly cold at Tahoe City during the first half of the month. On the 6th the temperature dropped to -13º, on the 7th it dropped to -15º, and on the 8th the morning low was -13º. The -15º on the 7th is the record low temperature for February at Tahoe City. Figure 7. Surface weather maps for January 25, 1949, 1:30 am EST and December 9, 1972, 7:00 am EST (pressure in millibars reduced to sea level). Maps courtesy of the NOAA Central Library Data Imaging Project. 17 DEGREE DAYS Many people find it useful to know how much warmer or colder it is compared to some standard temperature. Utility companies especially like to have some sort of number to use in determining how much power may be needed during periods that are colder or warmer than normal. An index that has been found useful is “degree days.” Degree days are based on the difference between 65°F and the average temperature of a day. The average temperature of a day is the average of the maximum and minimum temperature for that day. For example, if a day has a maximum temperature of 73°F and a minimum of 49°F, its average temperature is 61°F. Degree days are listed as either “heating degree days” or “cooling degree days,” depending on whether the average temperature is less than or more than 65°F. Degree days are calculated for a period of time (a month, for example) by calculating the differences between 65 and the average temperature of each day in that time period, and then adding up all the differences for days averaging above 65°F as cooling degree days, and all of the differences for days averaging below 65°F as heating degree days. Heating degree days provide an index of how much heating is needed to raise the temperature to 65°F, and cooling degree days provide an index of air conditioning requirements. Figure 8 and Table 2 show the average number of degree days recorded at Reno, Carson City, and Tahoe City for each month. More than 10 times as many heating degree days as cooling degree days are recorded at both Reno and Carson City throughout the year (Table 2). Almost no cooling degree days are recorded at Tahoe City. Average daily temperatures during the winter are often 30 to 40° colder than the degree day index base of 65º. High temperatures rarely reach 65º during the winter. However, during the summer at Reno and Carson City, even with afternoon readings in the 90s, temperatures can fall into the 50s at night, causing the average temperature for the day to approach 65º. Figure 8. Average number of heating and cooling degree days at Reno and Carson City, Nevada, and Tahoe City, California (1971–2000). Table 2. Average number of heating and cooling degree days at Reno and Carson City, Nevada, and Tahoe City, California (1971–2000). Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec Total Heating degree days Reno 984 756 683 502 285 91 12 22 130 416 732 987 5600 Carson City 972 755 682 507 306 110 11 27 149 433 733 976 5661 Tahoe City 1076 934 924 763 565 320 142 148 310 585 849 1055 7671 Cooling degree days Reno 0 0 0 0 11 72 204 164 41 1 0 0 493 Carson City 0 0 0 0 16 68 164 133 37 1 0 0 419 Tahoe City 0 0 0 0 0 2 20 21 4 0 0 0 47 18 Photo by Heather Angeloff Air pollution trapped under a temperature inversion over the Truckee Meadows. TEMPERATURE INVERSIONS AND AIR POLLUTION Inversions over the western Great Basin typically form in one of two ways. One way is through upper level subsidence. In an area of high pressure, air moves downward (subsides) and then moves outward when it reaches the ground. As the air subsides, it becomes warmer and also tends to dry out. The top of a subsiding layer of air travels relatively farther through the air mass than does the air in the lower part of the layer. Thus, this air at higher levels tends to warm and dry out at a faster rate than does the air below it. Because of this, the air that is higher up (and which travels farther) becomes warmer than the air below it. An inversion that forms from this process is called a subsidence inversion (Figure 9). The other method that can cause an inversion is through radiational cooling near the ground. At night, especially in regions that have dry air near the ground at high elevations, the ground starts to cool shortly after sunset as its heat is radiated into the air near the surface. In addition to the heat that is radiated into the atmosphere, additional heat is lost as the ground continues to cool during the night, and the air that is in contact with the ground cools as a result. A cold surface such as snow can cool the air in the lower layer of the air mass even more effectively than dry soil can. As a result of these processes, an inversion forms near the surface. Because this surface inversion is mainly caused by the loss of heat through the process of radiation into the atmosphere, it is called a radiation inversion (Figure 10). In the past air pollution has been a problem in the Reno area. Because of the topography of the area, pollution can remain over the region, sometimes for days at a time. The area from Reno and extending south to Carson City is situated between the Sierra Nevada and Carson Range to the west and the Pine Nut Mountains and other mountain ranges to the east. Because of the surrounding mountains, upper level winds do not always make it to the surface. The stagnant condition in the valley allows haze to remain. It often takes a shift in wind direction such as winds coming out of the south to mix the stagnant air and move it away. A cold front can also supply the stronger winds that can clear the pollution from the area. One thing that makes pollution so prevalent is the temperature inversions that are common over the area. An inversion is a layer of the atmosphere in which temperature does not follow its typical cooling pattern with increasing height. In an inversion, the air temperature increases with height (or does not decrease as quickly as it normally does). An air parcel that is forced upward remains cooler than the temperature of the air mass at that height. As a result, any rising air parcel remains denser than the surrounding air so it does not continue to rise, but eventually falls back to the surface. Inversions thus help to keep low level air near the ground and keep it from mixing with air at higher levels. This lack of mixing is what keeps the stagnant air trapped near the ground, and helps to keep any air pollution from mixing out and eventually dissipating. 19 Figure 9. A typical subsidence inversion over the Truckee Meadows. the “Washoe County AQMD is required by federal and state law to monitor and collect ambient Air Quality Data for pollutants deemed to be harmful by the U. S. Environmental Protection Agency (EPA)” (Washoe County Air Quality Management Division, 2002). The pollutants that AQMD monitors are: (1) carbon monoxide (CO); (2) ozone (O3); (3) particulate matter less than 10 microns in diameter, and less than 2.5 microns in diameter; (4) nitrogen dioxide (NO2); (5) sulfur dioxide (SO2); and (6) lead (Pb). One of the major constituents of pollution is automobile exhaust. The Reno and Carson City areas have experienced rapid growth during the last 15 to 20 years. The number of automobiles has increased substantially, but the physical dimensions of the surrounding topography have, of course, not changed. Thus, there are more pollutants being sent into the same amount of air. The AQMD estimates that approximately 94 percent of the CO emissions in the Truckee Meadows area are from motor vehicles. Carbon monoxide emissions have decreased during the last 15 years. During the early 1990s there were sometimes 15 Throughout the year, the air near the ground cools at night so radiation inversions are common. However, unless there is snowcover to keep the surface cold, the inversion dissipates during the day as the ground is heated, and mixing of the air can result. If high pressure is over the region, the descending air within this high can cause a subsidence inversion to form aloft. This type of inversion can be created at any time of year since it relies on the presence of an area of high pressure. The stable air associated with these inversions resists mixing, so the air mass does not change. Even if upper level winds are strong they tend not to mix down through this stable layer. Larger pollutants (such as those from dust storms and wildfires) eventually fall to the ground. However, smaller particles in gaseous emissions (such as from factories and automobile exhaust) remain in the atmosphere (Graedel and Crutzen, 1997). The Washoe County Air Quality Management Division (AQMD) monitors the level of pollutants in the atmosphere over the Reno area. According to an AQMD report, Figure 10. The development of a typical nighttime radiation inversion over the Truckee Meadows. 20 to 35 moderate to unhealthy CO days per year. By 2001 the number had dropped to fewer than five days per year. Ozone is another pollutant that can cause problems for people. Ozone is formed from the chemical reaction between hydrocarbons (molecules containing hydrogen and carbon) and NO2 in the presence of sunlight (Graedel and Crutzen, 1997). A large percentage of these hydrocarbons come from vehicle emissions. Even though vehicles are now checked annually for smog emissions, there has been little change in the number of days each year with moderate or unhealthy amounts of O3. During the 1990s there was an average of 80 days per year with O3 amounts rated as moderate or unhealthy. This lack of improvement may be because the increased number of vehicles during the last decade has offset the gains realized from emission testing. Particulate matter can be a problem in the areas in the lee of the Sierra Nevada. The large areas of sparse vegetation can provide plenty of dust and sand that can be suspended in the atmosphere. Even relatively small particles can decrease visibilities. Smoke, especially during the fire season, can also contribute substantial amounts of particulate matter. Smoke from wood-burning stoves is not as much of a problem now since their use has been restricted. The number of days per year that had moderate amounts of larger particulate matter (less than 10 microns) had decreased from around 50 per year in the early 1990s to around 10 days per year in 1998 and 1999. The number of days with unhealthy levels of these larger particulates has decreased from two to four per year to zero. Nitrogen dioxide is produced by automobiles and by industrial sources. The Washoe County AQMD continuously monitors two industrial sites in the Reno-Sparks area for NO2 emissions. The Truckee Meadows does not have as much of a problem with this pollutant as do many larger industrial regions. The emergence of a high tech component to Reno’s economy, and the area’s history as a warehousing and distribution center, may help to keep nitrogen dioxide levels relatively low in the future. The Washoe County AQMD states that sulfur dioxide and lead are not significant pollutants in the Truckee Meadows (Washoe County Air Quality Management Division, 2002). These substances are mainly produced by industrial processes. With the lack of heavy industry in the region, the levels of these pollutants are fairly low. The AQMD still monitors the levels of these substances, however. The AQMD reports that there has been an overall decline in pollutants such as carbon monoxide, ozone, and particulate matter during the last ten years. This can be attributed, at least in part, to many successful AQMD initiatives such as the use of oxygenated fuels in the winter months, the vapor recovery program for gasoline dispensing facilities, restrictions on residential wood burning, Federal emissions limitations on new cars, and vehicle inspections and maintenance requirements (“smog check”) (Washoe County Air Quality Management Division, 2002). The natural beauty that we see across our region should give us an incentive to make the air even cleaner. This will help to improve our already high quality of life. GROWING SEASON AND FROST Agriculture is a major part of Nevada’s economy. Although much of this industry is devoted to raising livestock, crop growing is also important. Because of the dry climate, most of Nevada’s farmland is irrigated. And this farmland is usually located in valleys. Hay, such as grass and alfalfa, is grown as cattle feed. Wheat, barley, oats, rye, and potatoes are some of the major crops that are grown throughout western Nevada. The Carson, Walker, and Truckee valleys contain much of the farmland. The Lake Tahoe basin is mostly forested and does not have nearly the percentage of farmland that western Nevada has. One of the reasons that the Tahoe basin does not have as many crops under cultivation is because of its relatively short growing season. The growing season is often defined as the average period of time between the last frost in the spring and the first frost in the fall. This can also be defined as the frost-free season (Trewartha and Horn, 1980). The growing season can also be defined as the length of time between the last occurrence of a certain temperature in the spring, and its first occurrence the following fall (Sakamoto and Gifford, 1970). Frost occurs when the temperature cools to the dew point and the dew point is at freezing or below. Water vapor sublimates directly out of the atmosphere and is deposited on cold surfaces as ice crystals. Air trapped in the ice crystals give the frost a whitish appearance. Frost that occurs for only a few hours at night may not be a big problem for agricultural interests. However, frost that occurs for much of the night can adversely affect plants. A killing frost can be defined as a frost period that “is sufficiently severe to end the growing season (or delay its beginning).” (Glickman, 2000). From the climatological record (for the period 1888– 1950) compiled by the U.S. Weather Bureau, the average date of the last killing frost in the spring in Reno was May 14. The average date of the first killing frost in autumn in Reno was October 6. The growing season in western Nevada can be shortened by a month or more by a late spring or early autumn frost. At Reno (for the period 1888–1950) the latest killing frost in the spring occurred on June 25, 1943, and the earliest killing frost in the autumn occurred on September 6, 1900. These dates have not changed appreciably during the last 100 years. Based on frost/freeze data from the period 1951–1980 (USDC, 1988), the average date of the last killing frost (temperature of 28°F or lower) at Reno occurs on May 12. The average date of the first killing frost occurs on September 30. At Carson City the average date of the last killing frost of the season occurs on May 11, and (like Reno) the average date of the first killing frost of the fall is September 30. At Tahoe City the date of the last killing frost in the spring is May 28. However, the relatively warm water of Lake Tahoe may extend the growing season a bit. The average date of the first killing frost in the fall at Tahoe City is October 2. The frost-free season lasts 120 to 130 days in valley locations in western Nevada. It can be significantly shorter at mountain locations with frost-free seasons of only 21 around three months in the upper elevations of the Lake Tahoe basin. In a study of frost-free periods at Reno extending from 1906 through spring 2006, it was found that the frost-free seasons have been getting longer during the past couple of decades. From 1990 through the spring of 2006 the date of the last 32°F temperature in the spring at Reno has been in April during nine of those seventeen years. The date of the first 32°F temperature in the autumn from 1990 through 2005 was in October during fourteen of those sixteen years. In fact, the first occurrence of a 32°F temperature in autumn 1992 was on November 3. This is the only time during the period 1906 through 2005 that the first freezing temperature in the autumn at Reno occurred in November (O’Hara, 2006). Still another way in which to define the growing season is through use of an index called “growing degree days.” The derivation of growing degree days (GDDs) is similar to that used to derive cooling degree days (CDDs) and heating degree days (HDDs). As mentioned in a previous section, both CDDs and HDDs use a base of 65°F in order to determine the need for air conditioning or heating in buildings. Growing degree days can be derived using any of a number of bases. Common base temperatures that are used are 40°F, 50°F, and (86–50°F). Each of these bases is discussed below. Photo by Larry Garside Sakamoto and others (1977) defined a growing degree day as a “unit based on the difference between a selected base temperature and the mean daily temperature.” The mean daily temperature is computed by adding the high and low temperature recorded for a calendar day, then dividing that sum by 2. For example, if the high temperature on a certain day was 72°F and the morning low was 36°F, then the average (mean) temperature for that day would be 54°F (72 + 36 =108, 108 divided by 2 = 54). By using a temperature base of 40°F there would be 14 GDDs for this day (54 - 40 = 14). If 50°F was used as the base, then there would only be four GDDs. Growing degree days can be used for many purposes. Sakamoto and others (1977) point out that vegetable canning companies can determine the number of GDDs that are needed for maturation of various vegetables. This can be more accurate than using a set number of calendar days. As mentioned in Sakamoto and others (1977), “[i]t is common knowledge that a cooler than normal spring or hotter than normal summer slows plant growth. Therefore, number of days to maturity based solely on calendar dates can be misleading” [italics theirs]. Another use of GDDs that they refer to is in the determination of the best times during which to apply pesticides. The University of Nevada Quadrangle and the Mackay Mines Building, January 22, 1997. 22 Photo by Mark Vollmer Rain showers during a summer storm as seen from the Tahoe Rim Trail about 9000 feet above sea level. Precipitation by Brian F. O’Hara and Tom Cylke RAIN rain shadow effect can be clearly seen as Reno and Carson City, in the valleys east of the Carson Range, receive less than a third of the precipitation that falls at Tahoe City, which is at a higher elevation in the Lake Tahoe basin between the Sierra Nevada and the Carson Range (Figure 12). Figure 13 on page 10 shows the average annual precipitation received across the eastern Sierra and western Nevada. Rainfall can occur across the region at any time of the year . Even during the winter, when a strong storm may be bringing heavy snowfall to the Sierra Nevada just west of Reno, rain may be falling in the Truckee Meadows. It is even possible for nothing to fall at Reno during significant winter storms. Moisture-laden air associated with the winter storm may deposit large amounts of snow on the western slopes and summits of the Sierra in California. The climate of western Nevada is one of the driest in the entire United States. Table 3 and Figure 11 show average monthly precipitation at Reno, Carson City, and Tahoe City. Reno averages only 7.48 inches of precipitation for the entire year, and Carson City receives slightly more at 10.36 inches. As in many parts of the western United States (west of the Rocky Mountains) western Nevada experiences a biannual precipitation pattern (Trewartha, 1981). Two-thirds of the precipitation falls as snow and rain during the colder half of the year. There is a secondary maximum during late spring when just around an inch of precipitation falls during May and June at both Reno and Carson City. It is clear that two-thirds of Tahoe City’s 32.66 inches of precipitation is also received during the colder half of the year from November through April. The Table 3. Average monthly and annual precipitation (inches) at Reno and Carson City, Nevada, and Tahoe City, California (1971-2000). Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec Total Reno 1.06 1.06 0.86 0.35 0.62 0.47 0.24 0.27 0.45 0.42 0.80 0.88 7.48 Carson City 1.82 1.66 1.26 0.42 0.52 0.40 0.22 0.32 0.51 0.69 1.26 1.28 10.36 Tahoe City 6.01 5.71 4.57 1.82 1.21 0.77 0.33 0.46 0.90 1.95 4.25 4.68 32.66 23 low pressure system forms at the surface. The subsiding air in this upper-level high pressure region suppresses the formation of clouds, and the clouds that do form tend to have high bases. Much of the rain that falls from these high-based clouds evaporates before it reaches the ground. As the high pressure area strengthens over Nevada during the summer the easterly winds south of the high pull moisture in from the Gulf of Mexico (and to a lesser extent from the Pacific Ocean and Gulf of California). This monsoonal moisture contributes to increased thunderstorm activity over the region. However, daytime temperatures are typically at their highest during July and August so, even with more rain showers and thunderstorms occurring, Figure 11. Average monthly precipitation (inches) at Reno and Carson cloud bases tend to be at their highest so City, Nevada, and Tahoe City, California (1971–2000). rainfall has even less of a chance of reaching the ground. This can explain why only ¼ However, most of the moisture may be wrung out of the air inch of rainfall is normally recorded at Reno and Carson mass before it reaches the valleys of Nevada east of the City during either July or August, the two driest months of the year. Sierra. The downward motion of the westerly winds Very little rainfall occurs during the warmer half of the coming off the Sierra crest causes the air to compress and year (May through October) in the eastern Sierra and become warmer. This makes it less likely that clouds will western Nevada. However, during intense thunderstorms, form, making the probability of precipitation even less. heavy rainfall can occur in a short period of time. The However, during the winter, storm tracks are often rainfall can also be extremely isolated. For example, on located across Nevada. As these winter storms move across June 21, 2002 only 0.10 inch of rainfall was reported at the the region the chance of precipitation occurring in the Reno official observation site at the Reno-Tahoe International area is the greatest. Three or four winter storms may move Airport. However, that evening, it was estimated that 2 across the region during just one month. The Reno area inches of rain fell between 6:20 and 7:20 pm in the Spanish may receive precipitation from each of these storms. Springs area northeast of Reno. As reported in Storm Data, During the summer the weather pattern changes. High damage at the new Spanish Springs High School was pressure moves north, which in turn pushes the storm estimated at over one-half million dollars (USDC, 2002). tracks to the north. Thus, western Nevada is not as much under the influence of persistent storms as it is during the Heavy precipitation of over one inch during a 24-hour winter. Snowfall can occur even into May (and very rarely period can be expected about once every year in western has been reported at Reno in June), but precipitation during Nevada. But these periods of heavy precipitation almost the warm half of the year (mid April to mid October) always occur during the colder half of the year (November occurs mainly as rain. through April). Tahoe City receives three to four times the High pressure forms aloft over the Great Basin during amount of precipitation that Reno and Carson City receive. the summer and, due to heating of the ground, a thermal This also is mainly from winter precipitation. Figure 12. Diagram showing rain shadow effect. Moisture in air mass is deposited as precipitation on windward side of barrier, leaving very little moisture to make it to leeward side. 24 Photo by Kris Ann Pizarro Stratocumulus clouds in foreground and snow on Carson Range, looking northwest from Washoe Valley. From 1906 through 2006, an inch or more of precipitation has been recorded at Reno on 54 days (O’Hara, 2006). On 13 of those dates precipitation totals of 1.50 inches or greater were reported. Some of the precipitation totals resulted from only rain. This is especially true during the warmer half of the year. However, during the winter, over an inch-and-a-half of precipitation can be recorded on a particular date, but some (or all) of it may be from snow. By contrast, since July 1, 1948, Carson City has recorded at least 1.50 inches of precipitation on 30 dates (mainly during the winter months). These data reflect the generally nighttime preponderance of precipitation during the colder half of the year. It should be noted that because Reno is an official National Weather Service (and earlier Weather Bureau) observation site, precipitation is measured once a day at midnight. However, at cooperative observation sites (staffed through the decades by volunteer cooperative weather observers), precipitation is not measured at midnight, but at other times. In the 1950s precipitation at Carson City was measured at 6 am local standard time (LST). In 2006 it was being measured at 5 pm LST. Thus daily amounts at locations with similar climates (such as Reno and Carson City) may show very different totals for the same date. This difference is clearly seen in the precipitation data for Reno and Carson City. The eastern Sierra and western Nevada experience a precipitation maximum at night during the colder half of the year (November through April) (Landin and Bosart, 1989). As a result, Carson City’s weather observations, which have been recorded at times other than midnight (usually in the morning or evening), would account for an entire nightly precipitation event. Reno’s daily precipitation observation, however, is always recorded at midnight (for the calendar day). Thus, an overnight precipitation event would be divided and recorded on two separate dates (before and after midnight) at Reno. This may be why Carson City has recorded so many more daily precipitation events of over 1.00 inch than Reno has. When Reno’s data are looked at in a timeframe that matches Carson City’s, both locations show similar totals (but with Carson City slightly ahead in average annual precipitation). With this diurnal nighttime maximum it would seem that Carson City’s precipitation data may give a better representation of the actual storm totals that are received in western Nevada. This difference in observation times should be kept in mind when comparing the precipitation data. Weather observers at Tahoe City, a cooperative weather observation site with a long history, have also measured precipitation at various times (in 2006 the daily weather observation was taken in the morning at 8 am LST). SNOW Snowfall is common across western Nevada during the winter. Snowfall amounts can vary widely both during a winter storm and throughout the entire winter (Figure 13 on page 10). Locations in the eastern Sierra Nevada can receive 2 or 3 feet of snow during a 24- to 48-hour period while the same winter storm may only drop a few inches in Reno or Carson City. At valley locations in western Nevada snow cover usually does not last very long, often completely melting within a few days. On an annual scale, snow cover throughout the winter can accumulate significantly in the Tahoe region with amounts measured in tens of feet by early spring. Figure 14 compares the snowfall and deepest snow depths recorded each winter at Reno and at the Central Sierra Snow Laboratory at Soda Springs, California, near Donner Summit. This location receives huge amounts of snow from powerful snowstorms coming in off of the Pacific. Reno, which is located in the lee of the Sierra Nevada and the Carson Range, receives only a fraction of the amount recorded near Donner Summit. This is because most of the moisture associated with a snowstorm oftentimes is wrung out of the air mass as it ascends the west slope of the Sierra Nevada. This moisture falls as snow (and as rain in the lower elevations) west of the Sierra crest with very little left over to be transported to the valleys east of the range. 25 Figure 14. Total snowfall and maximum snowpack depth at the Central Sierra Snow Laboratory near Soda Springs, California (1879–2003), and at Reno Nevada (1900–1995). Water years run from October through the following September. For example, Water Year 1900 is from October 1, 1899 to September 30, 1900. 26 Figure 15 and Table 4 show the average monthly snowfall reported at Reno, Carson City, and Tahoe City. The rain shadow effect mentioned above is even more pronounced in the snowfall data than it was in the precipitation data (which includes rainfall along with melted snowfall). Tahoe City receives over eight times the snowfall amounts recorded at either Reno or Carson City (Table 4). Snowfall has not been recorded at Reno during July and August and only a few times during June. No snowfall has been recorded at Carson City during these three months. However, at Tahoe City, snow is sometimes reported as late as June. Average annual snowfall at Reno and Carson City is almost 2 feet, almost all of it occurring between mid November and the end of March. Figure 15. Average monthly snowfall (inches) at Reno and Carson City, Nevada, and Tahoe City, California (1971–2000). Lake Effect Snow Western Nevada and northeastern California can occasionally experience lake effect snow under the right conditions, although not to the extent that areas in the lee of the Great Lakes do. Two of the necessary ingredients for lake effect snow are a cold air mass moving over a region and a relatively warm water surface. These conditions can be satisfied during the late fall and early winter as cold polar air masses invade the region. Three of the largest lakes in the area (Lake Tahoe, Pyramid Lake, and Walker Lake) can generate lake effect snow as cold air passes over them. In the fall, Pyramid Lake and Walker Lake can still be relatively warm, although due to their relatively shallow depth they cool down fairly rapidly as the winter progresses. Lake Tahoe, being over 1500 feet deep over much of its extent, does not cool down as rapidly. The difference in temperature between the relatively warm water surface of Lake Tahoe and a cold air mass moving across it can provide the instability necessary to promote the formation of clouds and snowfall downwind of the lake. Lake Tahoe, Pyramid Lake, and Walker Lake are much smaller than the Great Lakes. For lake effect snowfall to be generated by these lakes, the air moving across them must have a trajectory that will pick up as much moisture as possible from the lake surface. This can happen when the wind flow is out of the northwest when it crosses Pyramid Lake. This takes the cold air along the long axis of the lake bringing the air and warmer water surface in contact with each other for the longest period possible. If the wind is out of the west or southwest the residence time of the air may not be long enough to generate many clouds, let alone snowfall downwind of the lake. Walker Lake, the smallest of the three lakes, is about 20 miles long along its north-south axis but less than 10 miles wide at its widest point. Like Pyramid Lake, lake effect snow is more likely downwind of Walker Lake when the wind flow is from the north or south along its longest axis. Lake Tahoe is 22 miles long in its north-south axis and 12 miles wide in its east-west axis. This is slightly larger than the northern part of Pyramid Lake. However, the topography around Lake Tahoe is much steeper than that around either Pyramid Lake or Walker Lake. The mountains around Lake Tahoe can combine with the relatively warm lake surface to produce impressive bands of lake effect snow downwind of the lake. Washoe Valley can be impacted if the wind is out of the west. The air moving over Lake Tahoe picks up moisture, the mountains to the east help to intensify the snowfall that is generated, and the snow is then carried eastward and deposited not only on the Carson Range but on Carson City and the surrounding areas as well. When added to snow from a previous snowstorm the snow cover can accumulate to impressive amounts. A half of a foot of snow can fall within a few hours from a lake effect snow event. An impressive lake effect snow event occurred in early November 2000 when 23 inches of snow generated by Lake Tahoe fell across the Carson City area (Cairns and others, 2001). Due to the small scale of many of these lake effect snow events, radar remains one of the best methods of tracking and forecasting their extent (Huggins and others, 2001). Table 4. Average monthly and annual snowfall (inches) at Reno and Carson City, Nevada, and Tahoe City, California (1971–2000). Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec Total Reno 5.2 5.4 3.3 0.9 0.7 Trace 0.0 0.0 0.1 0.5 3.1 4.3 23.5 Carson City 6.3 4.0 3.2 1.1 0.5 0.0 0.0 0.0 0.1 0.2 1.2 4.6 21.0 Tahoe City 42.7 37.6 34.7 16.0 3.7 0.2 0.0 0.0 0.3 2.3 16.2 35.3 188.9 27 Photo by John James Snow in the Sierra. Deep snow cover at Meyers, California during April 1969. Historic Snowstorms January 10–14, 1911. This was the greatest snowfall in Reno from a single snowstorm since 1890. A total of 37.9 inches of snow fell from the 10th to the 14th. The 19.7 inches falling on the 12th is still the second greatest 24-hour amount to ever fall in Reno. Trains and street cars were unable to operate for 2 weeks following this storm. Photo by Jennifer Mauldin January 17–18, 1916. A record 22.5 inches of snow fell on January 17 in Reno, with a 25.5 inch storm total by the 18th. This was the biggest of several storms during the month that led to an all-time monthly record in Reno of 65.7 inches of snowfall. Figure 16 shows the area of low pressure over the California coast on the morning of January 17. This low moved through the Sierra and western Nevada, and deposited the huge amounts of snow that were reported. The 199 inches of snow measured at Marlette Lake in the Carson Range east of Lake Tahoe set an alltime monthly record for the state of Nevada. Temperatures dropped to a record -17° in Reno on the 21st following this snow storm. December 1–5, 1919. Five consecutive days of snowfall totaled 33.6 inches for the biggest single December storm in Reno’s history. Cold temperatures kept snow on the ground until the 27th. February 9-11, 1922. A total of 27.4 inches of snow fell in Reno during this 3-day period. Even more fell in the Sierra with 78.0 inches being reported at Tahoe City. Snow and avalanches in the Sierra halted rail traffic at Reno until the 14th. Snowfall in north Carson City as a result of a lake effect snowstorm from Lake Tahoe during the winter of 2000– 2001. The actual depth of the lake effect snowfall from this storm can be seen from the snow on the roof. January 10–17, 1952. This snowstorm recorded 11.8 feet of snow at Donner Summit over the 8-day period. On January 13th the Southern Pacific luxury streamliner City of 28 Monday, January 17, 1916 Figure 16. Surface weather maps for January 17, 1916, 8:00 am EST; January 12, 1952, 1:30 am EST; and December 25, 1971, 7:00 am EST (pressure in millibars reduced to sea level). Maps courtesy of the NOAA Central Library Data Imaging Project. 29 falling at Carson City. However, larger amounts were measured in the Sierra with 44.0 inches of snowfall at Tahoe City from the 25th through the 30th. Close to 5 feet of snow fell at Truckee during these dates. Photo courtesy of the Nevada Historical Society December 21–28, 1971. This Christmas storm dropped 25.6 inches of snow in Reno over 8 days, and the 14.9 inches on the 25th is the sixth largest 24-hour amount since 1890. The cold front that moved through the region on December 25 (Figure 16) brought in an arctic air mass. The very cold temperatures that followed this storm lasted into early January, and helped to keep several inches of snow on the ground until January 19. January 4-5, 1982. This storm set a Nevada 24-hour snowfall record of 48 inches at Daggett Pass on the southeast side of Lake Tahoe. During this two-day period 29.0 inches of snow fell at Tahoe City. At Carson City 13.0 inches of snow was reported. Milder temperatures brought a mixture of rain and snow to Reno during this period with 3.8 inches of snow falling there on the 5th. Snow cover in Reno in the winter of 1915–16. San Francisco was trapped by a snow slide on Donner Summit. As a result, 226 passengers were stranded for three days until they were allowed to walk a half mile to the newly plowed Highway 40. This was “the first time since the exceptionally snowy season of 1892 that the tracks of the Southern Pacific Company through Donner Pass had been blocked for any considerable period” (Ludlum, 1952). Figure 16 shows the cold front that moved through the Sierra Nevada on January 12. This cold front helped in depositing the huge amounts of snow reported across the region. Almost 14 inches of snow fell in Reno, and up to 3 feet fell in outlying areas. Fifty-five mph winds blew drifts up to 15 feet high in Washoe Valley and north of Reno, stranding many vehicles north and south of Reno. The Mount Rose highway was closed for six weeks, and Donner Summit was impassable to auto traffic. Skiers were stranded and had to be rescued at the Mount Rose and Sky Tavern ski areas. The only way in and out of Reno was east to Fallon which reported surprisingly little snow. November 8–12, 1985. A total of 16.3 inches of snow fell in Reno over this 5-day period. The 15.2 inches of snow that fell in Reno on the 10th set a November 24hour snowfall record. It is also the fifth largest one-day snowfall total recorded in Reno since 1890. Snow remained on the ground until Thanksgiving. February 13–18, 1990. Snowfall from this 6-day storm totaled 21.5 inches in Reno. Eighteen inches of this total was measured on the 16th, setting a 24-hour record for February, and going down as the third largest single day January 24-30, 1969. Over a threeday period from January 24 to 26, a total of 10.4 inches of snow fell in Reno, with 11.0 inches of snow Photo by Kris Ann Pizarro February 7-12, 1959. This six-day storm dropped 22.1 inches of snow in Reno. The total of 13.2 inches that fell on the 10th is the ninth largest 24-hour snow amount ever recorded in Reno. During this same six-day period 16.9 inches of snow fell at Carson City, with 44.0 inches reported at Tahoe City. Snow cover in Reno in February 1990. 30 snowfall amount at Reno since 1890. Figure 17 shows the weather map for February 16. The cold front over northeastern California moved through the Sierra and western Nevada during the day. December 30, 2004–January 1, 2005. This was the first of two major snowstorms in as many weeks to affect the region. This first storm dropped nearly 2 feet of snow on the Reno and Carson City areas. Over 5 feet of snow fell in the higher elevations of the Sierra. On December 30 it was estimated that 16.4 inches of snow fell in Reno, with an additional 4.9 inches falling on the 31st and another 0.6 inches falling on January 1. The snowfall had to be estimated because the cooperative weather observers, due to the impassable roads, could not make it into Reno to make measurements. The National Weather Service and the Western Regional Climate Center estimated the snowfall from daily precipitation received at the Reno airport, and from snowfall, precipitation, and snow density measurements recorded at other locations across the RenoCarson City area. The 16.4 inches of snowfall that was estimated for the 30th would make that the fourth largest daily snowfall amount reported in Reno in the last 100 years. The weather map for December 30 in Figure 17 shows the cold front which moved through the region and deposited the near-record snowfall amounts. A second snowstorm dropped another 16.4 inches on Reno on January 7 and 8. By January 8, 20 inches of snow cover was reported in Reno. As a result of the two storms a total of 79 inches of snowfall was reported at the National Weather Service Forecast Office in the foothills north of Reno. Similar totals were reported in the foothills west of Reno at elevations of around 5000 feet. Nearly two feet of snow cover paralyzed the valleys of western Nevada for much of the month of January. Up to 3 feet of snow cover was common in the foothills west of Reno and Carson City. The snow depth remained at least a foot in Reno through January 15 and was not completely gone until February 1. Snowfall in the Lake Tahoe basin above 8000 feet elevation totaled 10 to 15 feet from the two storms combined. The snowfall and snow cover that resulted from these two storms were the most seen in the region since the incredible series of four snowstorms in January 1916. Snow Cover Figure 17. Surface weather maps for February 16, 1990, 7:00 am EST and December 30, 2004, 7:00 am EST (pressure in millibars reduced to sea level). Maps courtesy of the NOAA Central Library Data Imaging Project. 31 Even though the Reno and Carson City areas receive an average of almost 2 feet of snow annually, snow usually does not last on the ground very long. Due to the mild daytime temperatures, and the generally sunny skies during the winter months, snow cover usually completely melts after just a few days. Snow depths rarely exceed 6 inches because snowstorms in the Reno area normally do not deposit this much snow. Large amounts of snow can be deposited in the Sierra Nevada Photo by John James Snow cover at South Lake Tahoe during late winter, 1969. Homes were damaged from 15-foot snowpack and 20-foot drifts. Historic Winters Winters are typically cold in western Nevada and the Sierra Nevada, and snow can be expected, especially in the Sierra, every winter. However, some winters are more severe than others due to greater amounts of snow or colder temperatures, or both. Listed below are some of the winters that have stood out as being especially severe. but by the time a storm system reaches the valleys east of the Sierra Nevada most of the precipitation has been wrung out of the air mass. Relatively little moisture is left that can be deposited as snow (or rain) in the lee of the mountains. The higher elevations of the Sierra receive much more snowfall than the drier valleys to the east. A total of 300 to 400 (or more) inches of snow can fall at some of the ski resorts around the Lake Tahoe basin during a typical winter. As this snow accumulates throughout the winter its depth can reach ten feet by the middle of March. This can be great for the ski slopes but it must be cleared from streets and sidewalks. The deepest snow cover ever recorded in the 48 contiguous United States occurred at Tamarack, California (southwest of Lake Tahoe) on March 9, 1911 when 454 inches (almost 38 feet!) of snow was measured (Wisler and Brater, 1959). This was after receiving 390.0 inches of snow in January 1911 (a U.S. record) (Ludlum, 1982). Deep snow cover does not prove to be an inconvenience very often for residents of the Truckee Meadows and Eagle and Carson Valleys. However, there have been some periods when snow cover has lasted for over a month. And deep snow cover has sometimes lasted for well over a week. Deep snow cover can be expected every winter in the Tahoe Basin and residents there prepare for it and are used to it. The deepest snow cover reported at Tahoe City since 1931 was the 166 inches that was on the ground on March 20, 1952. 1889–90. This turned out to be a record-breaking winter. Temperatures were near normal through late autumn and through most of December. A total of 5.7 inches of snow was reported at Carson City on December 23 with another 10.1 on the 24th and 4.9 inches on the 25th. A strong cold front moved through the evening of the 28th. After the front passed, the temperature dropped to -7° the morning of the 29th. The temperature was still -1° at 1:30 that afternoon but finally rose to 15° that evening. The total snowfall for December at Carson City was 31.4 inches. The snowy pattern continued into January with 10.0 inches of snow falling at Carson City on the 3rd as a cold front moved through. Very cold air settled over the region. The low temperature on the morning of the 6th was -10º and it only got worse. The morning low was -17° on the 7th and -22° on both the 8th and 9th. There was even a report of the low at Carson City reaching -27° on January 8. At Reno the temperature bottomed out at -19° the morning of the 8th. This remains the all-time record low at Reno. Snow returned to the region in mid January and 20.1 inches fell at 32 Photo courtesy of the Nevada Historical Society Carson City on the 17th. The total snowfall for the month at Carson City was 55.1 inches. Warmer weather in late January and early February helped to melt much of the snow. Mild weather continued through the first half of February. Then over a period of four days (the 16th through the 19th) a total of 22.7 inches of snow fell at Carson City. On the 25th very strong winds blew the snow into drifts, blocking the Virginia and Truckee Railroad for two days. Total snowfall at Carson City during February was 26.9 inches. On the morning of the 27th the temperature fell to -3º at Carson City. The winter was severe across the entire state of Nevada. Temperatures in January fell to -42º at Elko and -39º at Beowawe. Farther south at Ely the lowest temperature during January was -27° and at Eureka the thermometer hit -26º. February was also cold. The lowest temperatures recorded for the month were -41º at Elko, -20º at Beowawe, -23º at Ely, and -19º at Eureka. Across northern Nevada the harsh weather took a toll on livestock on the open range. Commercial Row at Southern Pacific Railroad Depot in Reno during the winter of 1915–16. 1915–16. The winter of 1915–16 started out as fairly mild. Cold temperatures did not invade the region until the last week of December. A snowstorm moved through the Sierra the first week of January dropping 31.0 inches of snow on Tahoe City on January 3. Temperatures stayed above zero in western Nevada until the second week of January when a snowstorm moved through the region dropping 13.8 inches of snow on Reno. On the morning of the 11th a low of -1º was reported at Reno. The temperature fell to -9° the following morning. At Tahoe City the temperature dropped to -14° on the morning of the 11th and -8º on the 12th. A week later an even bigger snowstorm dumped 22.5 inches of snow at Reno on January 17 and another 3.0 inches on the 18th. The 22.5 inches of snow that fell on January 17 remains the all-time largest single day total for Reno. Travel was at a standstill. Railroad passengers were stranded at Reno, Carson City, and other locations because trains could not make it through. Temperatures at Reno fell to -11° on the 20th and -17° on the 21st. Still another snowstorm later in the month dropped 14.7 inches of snow on Reno over a three-day period (27th through the 29th). The thermometer plummeted again with lows of -4° and -13° being reported at Reno on the 30th and 31st, respectively. At Tahoe City the temperature dropped to 15° on the 30th and it was -14° the morning of the 31st. The 65.7 inches of snow that fell at Reno during January 1916 is still the all-time record monthly total for the city. Record snow cover during January made travel nearly impossible. After the snowstorm, during the second week of January over a foot of snow was on the ground at Reno. As a result of the 22.5 inches of snow that fell on the 17th, a record 30 inches of snow depth was reported in Reno. The snow depth did not drop below 10 inches for more than a week. The big snowstorm during the last week of the month brought the snow depth back up to a foot and a half. February was relatively mild and the warmer temperatures caused most of the snow at Reno to melt by the middle of the month. 1936–37. Conditions were fairly mild until late December when a total of 14.2 inches of snow fell at Reno from the 27th through the 31st. A second snowstorm during the first week of January brought much colder temperatures. The low temperature dropped to zero at Reno on the 6th. The temperature dropped to below zero on each of the next seven mornings. The low on the morning of the 8th was -16º and the low on the 9th was 14º. Snow cover of nearly a foot helped to keep conditions cold across western Nevada. At Tahoe City it was -9º on the mornings of January 7 and 8th, and -14º on the 9th. A cold front in mid January did not bring much snow but it reinforced the cold temperatures. At Reno the morning lows were -12° on the 20th and -14° on the 21st. It was also cold at Tahoe City where the temperature dropped to -13° on the 20th and -14° on the 21st. The coldest temperature reported in the region was at Boca, California (in eastern Nevada County northeast of Truckee). On the morning of the 20th the temperature dropped to an incredible -45°! This remains the all-time record coldest temperature for the entire state of California. A significant snowstorm in late January brought 17.0 inches of snow to Reno over a three-day period (28th through the 30th). Nineteen inches of snow covered the ground at Reno on January 30. However, as in the severe winter of 1915–16, mild weather in February helped to melt the snow in the valleys of western Nevada so that most of it was gone by the middle of the month. 1948–49. Cold temperatures were the main problem during the winter of 1948–49 in a region stretching from the western Great Basin to the Rockies. January 1949 ranks as the coldest January on record in Reno. December 1948 is the sixth coldest December on record in Reno, and February 1949 is the eighth coldest February ever. December 1948 was not especially snowy in the valleys east of the 33 Reno were still cold for late March. On the 20th, 21st, and 22nd the temperature dropped to 6º, 1º, and 5º, respectively, still all-time record lows for those dates in Reno. On those same dates at Carson City, the morning lows were 4º, -5º, and -2º, also record lows for those dates. It was -5º at Tahoe City on the morning of the 20th. Sierra. The largest daily snow amount at Reno was 3.5 inches that fell on December 26. However, at Tahoe City, 36.0 inches of snow fell on December 14. A cold air mass settled over the region and morning lows in late December were barely above zero. The very cold weather continued through January; 21 of the 31 days had morning lows below zero at Reno. Two snowstorms, one in early January and one in mid January deposited only around 5 inches of snow each, but the very cold temperatures kept this snow on the ground through January and the first half of February. At Reno the morning low was -16° on January 25 and -15° the next day. These remain some of the coldest days on record in Reno. Five days in February also had lows below zero at Reno. In Carson City the temperature dropped to -16º on January 25 and to -20º on the 26th. This -20º reading is the record low temperature for January at Carson City (using official weather data for Carson City starting on July 1, 1948). The very cold conditions were also felt across much of the rest of Nevada. Because of the deep snow cover over much of northern and central Nevada, livestock on the open range were stranded. Ranchers had difficulty getting food to their livestock and 10 to 25 percent of the animals died (Houghton and others, 1975). In what became known as “Operation Haylift” hay was dropped from airplanes in order to feed the isolated cattle. 1968–69. This was a snowy winter across the Sierra and western Nevada. Three snowstorms in December dumped almost ten inches (9.1 inches) of snow on Reno, with larger amounts in the Sierra and Carson Range. The snowy conditions continued into the next year. A snowstorm in late January dropped 10.4 inches of snow on Reno. In the Sierra (at Tahoe Meadows) 37 inches of water equivalent fell as snow during the month of January (a record for Nevada). February saw even more snow. The 23.5 inches of snow that fell in Reno in February makes this the fourth snowiest February in Reno’s history. Heavy snowfall also occurred in the mountains. The Mt. Rose Highway was closed for six weeks from late January to early March due to the deep snow. On March 1 the snow depth at Tahoe Meadows was 14 feet 7 inches (also a record for Nevada at that time). The winter turned out to be near average in temperature. In fact, relatively warm conditions in early January helped Reno record an average temperature for the month (37.0°) that was 6.6 degrees above normal. 1951–52. This was a very snowy winter in the Sierra Nevada. A snowstorm in mid January made travel in the Sierra impossible because roads and railways were blocked by snow. In Reno 13.8 inches of snow fell from January 11 to 16. At Tahoe City 42.0 inches fell on the 15th alone. Average daily temperatures at Reno were more than 10° below normal from January 16-19 with low temperatures of -2° on the 17th and -4° on the 19th. The snow was especially deep at Lake Tahoe. Over 3 feet of snow (38 inches) was on the ground on December 7. It only increased from there. By December 31, 78 inches of snow cover was reported at Tahoe City (still a record snow depth for that date). On January 12 there was 110 inches of snow on the ground, and it increased to 120 inches (10 feet) by January 17. February did not see many problems but snow returned in March. Through most of February temperatures were near normal and snow did not accumulate in the valleys of western Nevada. The snow was deeper in the Sierra; the snow depth at Tahoe City remained around 10 feet throughout February and into mid March. On March 14 a powerful snowstorm deposited 13.6 inches of snow at Reno, and another 3.5 inches fell the next day. At Carson City 14.5 inches fell on the 15th. The morning low at Reno was 3° on the 16th and 9° on the 17th. These are still the record lows in Reno for those March dates. A total of 5.9 inches of snow fell on the 18th and 19th at Reno, and on the 19th and 20th, 8.5 inches fell at Carson City. At Tahoe City 28.0 inches fell on the 19th. The next day (March 20) 166 inches (13.8 feet) of snow was on the ground. This is the greatest snow depth ever recorded at Tahoe City. The snow cover kept conditions cold. Even though they did not drop below zero, the morning lows at 1992–93. An impressive period of deep snow cover occurred from late December 1992 through all of January 1993. Even though the total period of time was just over a month, on 20 of those days at least 5 inches of snow cover was reported at Reno. And at least 10 inches of snow was on the ground on 11 days at Reno. The period started with an impressive snowstorm that dumped 12.9 inches of snow on Reno from December 28 to 30. At Carson City 17.0 inches of snow fell on the 29th and 30th. At Tahoe City, 76 inches of snow was on the ground on January 1. A series of storms through the first half of January continued to add to the snow cover, and cold weather kept the snow from melting. The temperature at Reno dropped to -3º the morning of January 3rd and -1º the next day. A low of -1º was reported again on January 12. At Carson City the temperature dropped to -1º on the 11th and to an impressive -14º on the morning of the 12th, record low temperatures for those dates. A snowstorm the first week of January dumped 8.1 inches of snow at Reno, and by January 8, a total of 10 inches of snow was on the ground. Except for two days (January 9 and 15), at least 10 inches of snow cover was reported each day at Reno from January 8 through the 20. Warm weather late in the month finally started to melt the deep snow cover. 2004–05. Autumn 2004 did not portend the incredible winter that would unfold in December. A snowstorm on November 27 dumped 7 inches of snow on Reno—not an unusual occurrence. Cold air filtered into the region with average temperatures 15 to 20° below normal in late November and early December. Temperatures the rest of the month were near normal but things were about to change. 34 Photo by Christine Mauldin Snow cover in Carson City, winter of 1992–1993. From December 30 through January 1, historic amounts of snow fell on the region. Nearly 2 feet of snow fell in Reno and Carson City. Three to 5 feet of snow fell in the foothills of the Carson Range and 6 to 8 feet in the higher elevations of the Sierra. A second snowstorm moved through the region a week later, depositing almost as much snow as the earlier storm did. The region was paralyzed by this almost unprecedented series of snowstorms. The only thing comparable was the series of four snowstorms that moved through the region during January 1916. Temperatures were below normal throughout the month of January but not as cold as some other winters. Average daily temperatures during the month were below normal for all but five days at Reno. The deep snow cover helped to keep temperatures low. The snow also contributed moisture to the lower atmosphere through evaporation and melting during the day. The temperature inversion that formed kept this moisture near the surface and dense fog was reported through most of the last half of January and into the first week of February. This dense fog, like the heavy snowfall that preceded it, was almost unprecedented. Dense fog was reported at Reno for nine consecutive days in late January and for another five consecutive days in early February. On only two other occasions in the last 60 years had dense fog been reported for nine consecutive days or longer. In addition to the nearly unprecedented snowfall and dense fog, an ice storm occurred on January 25—a relatively rare event for the Truckee Meadows. The rest of the winter was near normal, which seemed like a relief to many residents of the region. Both February and March had near normal temperatures and precipitation. But memories of the incredible pair of snowstorms that visited the region in late December and early January will probably remain with many residents for years to come. ICE STORMS Ice storms are usually not a major problem in the RenoCarson City-Lake Tahoe region but they can occur, as was experienced in late January 2005. Ice storms are more prevalent farther to the northeast in places such as the Winnemucca area. The publication Storm Data did not list any significant ice storms in the Reno-Carson City-Lake Tahoe area for the period 1959 through 2004 (USDC, 1959 -2005). For ice pellets (sleet) or freezing rain to occur at the surface there has to be a layer of cold air (temperature below freezing) at ground level with a layer that is warmer than freezing above it. Snow that falls into the warm layer melts into raindrops and these raindrops then freeze as they pass through the cold layer of air at the surface. If the cold layer is deep enough the raindrops will freeze into ice pellets. If the cold layer is fairly shallow the raindrops will not have time to freeze but will freeze when they come into contact with structures, trees, and other vegetation that are below freezing. 35 Photo by Heather Angeloff Fog over the Truckee Meadows, looking southwest toward Mount Rose. Humidity by Brian F. O’Hara Even though western Nevada has a dry climate, relative humidity typically varies throughout the day. This diurnal variation is mainly the result of changes in air temperature. The relative humidity, however, can also respond to changes in moisture in the lower atmosphere. This process can be seen in the data for Reno in Figure 18. For any month throughout the year, the highest relative humidity is recorded when the air temperature is at its lowest, typically near sunrise. Similarly, the relative humidity is at its lowest in the late afternoon or early evening when the air temperature is at its highest. The relative humidity is higher during the winter because the amount of water vapor in the air does not vary as much as the temperature does throughout the year. The air mass over western Nevada is fairly dry throughout the year. Additionally, the air is quite warm during the summer and cold during the winter. However, it is not correct to say that the warmer air during the summer can hold much more moisture than the cold air of winter can. Bohren and Albrecht (1998) point out that a change in relative humidity is the result of changes in evaporation and condensation, not an air mass’s supposed ability to “hold” moisture. When the air temperature is higher than the dew point temperature there are more water molecules in the air mass that are evaporating than are condensing. As an air mass cools, its molecules have less energy (are less energetic) and so, by moving more slowly, have a better chance to condense. When the air temperature equals the dew point temperature there are approximately the same number of water molecules evaporating as are condensing. Thus, since the moisture does not vary much throughout the year over the western Great Basin, the air is closer to saturation during the winter than it is during the summer since the wintertime temperature is closer to the dew point temperature. This is why the relative humidity is higher during the winter than during the summer. But a change in temperature is not the only thing that can affect relative humidity. A change in the moisture content of the air mass can also change the relative humidity. The Southwest Monsoon is a phenomenon that affects relative humidity during the late summer over the Great Basin. During the late summer, southerly winds from the Gulf of California and Pacific Ocean (and even from the Gulf of Mexico) transport moisture across Arizona and into the Great Basin. This added moisture can contribute to afternoon thunderstorm development, especially over the eastern Great Basin (Whiteman, 2000). This thunderstorm development can also extend into the western Great Basin. Due to the monsoon, humidity values can also increase (Figure 18). After reaching an annual minimum during the day and night in July, the relative humidity starts to increase in August. Late summer temperatures can also be affected. The additional cloud cover that results from the monsoonal moisture and the afternoon thunderstorms in late summer also helps to keep average temperatures lower than those recorded during July. FOG Fog forms as a result of condensation exceeding evaporation in an air mass. Water vapor is added to the air either from being evaporated from a water surface, or by being advected (moved into a region by wind flow), thus making the resident air mass more moist. When an air mass is saturated, this means that condensation equals evaporation at that temperature and pressure. If additional water vapor is added to the air (either through evaporation or advection) then water molecules are forced out of the air and they become suspended as fog droplets. Visibility may be fairly good if the fog is just starting to form. If additional water vapor molecules are not forced into the air mass, then the fog may remain relatively light 36 Figure 18. Average daily variation in relative humidity at Reno, Nevada (1971–2000). 37 Photo courtesy of the Nevada Historical Society Pogonip along the Truckee River (c. 1910). with no decrease in visibility. However, if water vapor is continually added to the air mass, or if the temperature of the air continues to drop (or a combination of the two) then fog can become denser. Visibilities can decrease rapidly if moisture is added to the air mass quickly or if the temperature drops quickly. Dense (sometimes referred to as “heavy”) fog is defined by the National Weather Service as fog restricting visibility to ¼ mile or less. Dense fog is not a significant hazard in Reno (Figure 19). Fog is mainly a wintertime phenomenon. During the summer the air mass is usually very dry. Even as the temperature drops at night the air mass does not get very close to being saturated. In July the dew point may be 15º F. The air temperature may be in the 90s during late afternoon and drop into the upper 50s at night. Since the atmospheric moisture does not change appreciably, the relative humidity stays low. During the winter, the dew point may also be 15º F. However, the air temperature may drop to 15º or less at night. In this situation the air may become saturated. With any additional cooling water vapor would condense out of the air mass and fog could start to form. Snow cover could contribute to the formation of fog as the snow on the ground evaporates moisture into the relatively dry air mass above it while simultaneously cooling the air. Dense fog can form this way. In the valleys of western Nevada this may happen, on average, on two or three days during both December and January. Longer periods of dense fog however, are relatively rare. This usually requires snow cover in order to produce the evaporation that would cause fog to form for many nights in a row. Since the winter of 1948–49 dense fog (restricting visibility to ¼ mile or less) has formed for five or more consecutive days on only 10 occasions. Two of the periods of five or more consecutive days of dense fog occurred after the two historic snowstorms that moved through the region in late December 2004 and early January 2005. FREEZING FOG (POGONIP, RIME) Fog mainly occurs during winter nights when the temperature drops to the dew point. Often the dew point will be below freezing and the fog that forms under these conditions is referred to as freezing fog. The accumulation of ice, or rime, which results from freezing fog, coats plants or any other surface that is colder than freezing. In Nevada, this rime is sometimes called pogonip. Houghton and others (1975) stated that the term pogonip is thought to come from the Paiute word “meaning ‘white death.’ The cold, damp conditions accompanying these fogs made the people more susceptible to illness in the outdoor environment.” Figure 19. Average number of days with dense fog (visibility ¼ mile or less) at Reno, Nevada (1943–2004). 38 Drought and Evaporation by John W. James and Gary Barbato DROUGHT cant portion of the water that is used in this region. During wet periods there is plenty of runoff to keep Lake Tahoe high. During normal periods Lake Tahoe is not usually below its rim (elevation: 6223.0 feet) but, during dry periods, the surface of Lake Tahoe sometimes falls below its natural rim. Thus, Lake Tahoe’s elevation can be a good indicator of whether the region is suffering from a drought or not. Figure 20 shows how the level of Lake Tahoe has fluctuated throughout the twentieth century. The severe droughts of the mid 1920s to mid 1930s, the mid 1980s to mid 1990s, and the early 2000s can clearly be inferred from the graph. Nevada is typically dry, but we usually don’t consider the lack of moisture a significant problem until we experience conditions that are abnormally dry, such as when the water level in wells starts to drop, or the price that we pay for water goes up (this is a concern that many people in the eastern United States may never think about). Drought is common in the region during the warmer half of the year (April through September). However, midwinter droughts have the most significant impacts on the region because of the dependence on snowpack runoff from the Sierra Nevada for water supplies. Reno has an average annual precipitation of only 7½ inches, and only 50 rainy days per year (a rainy day is defined as a day with at least 0.01 inches of rain). It is even drier in Las Vegas, with an annual precipitation of only 4 Webster’s Dictionary defines drought as “a long spell of dry weather.” If that definition is correct, then most of the arid Southwest is usually in year-round drought. Perhaps a more accurate definition is found in the Glossary of Meteorology (Glickman, 2000), which defines drought as a “period of abnormally dry weather sufficiently long enough to cause a serious hydrological imbalance.” This seems closer to what we think about when we talk about drought. However, Landsberg (1982) stated that “[n]o universal definition of drought exists, although there are a number of localized definitions for various geographical areas, usually geared to such aspects as crop yields, reservoir levels, or stream flow.” For example: the wettest water year in Reno was 1889–90 when 16.39 inches of precipitation fell. If only 16.39 inches of precipitation fell at Tahoe City, it would be the fourth driest water year on record there (the driest water years on record were 1976– 77 (8.82 inches), 1986–87 (14.37 inches), and 1975–76 (15.58 inches)). (A water year is defined as the 12-month period from October 1 to September 30 of the following year. A water year is often designated by the year in which it ends: for example, the 1977 water year extended from October 1, 1976 through September 30, 1977.). Reservoir (or lake) levels seem like a good measure of the availability of moisture in the eastern Sierra and western Nevada. The Lake Tahoe basin supplies a signifi- Figure 20. Monthly surface elevation of Lake Tahoe (1900–2004). 39 strict conservation measures concerning the water balance (precipitation/evaporation ratio), can lessen the problem. Redmond (2003) stated that “in the Southwest the regional water allocation and distribution system has not been tested by a major drought within the residence time of a large fraction of the current population.” inches and 25 rainy days per year. In the Greater Reno and Carson City area, with well over a half-million people, water is supplied by rivers flowing down the eastern slopes of the Sierra Nevada, and from deep wells. Neither of these sources is sufficient during times of drought. For example, in the spring of 2004, Lake Mead dropped to its lowest level since the mid 1960s. Lake Tahoe also responds to drought, as Figure 20 shows. Other, smaller lakes, certainly respond to drought. The photos on page 11 show Washoe Lake when it was nearly completely dry in 2004 and when it had filled again in 2006. Dry weather and population demands on water have greatly increased in the past twenty years in western Nevada and the Lake Tahoe region. Thus, such a definition of drought as noted in the dictionary is not sufficient, and much refinement is needed in order to fit regional differences. Most of Nevada is semiarid, and periods of drought only exacerbate the problem of lack of water (upper photo on page 41). But drought can also affect the higher elevations (lower photo on page 41). Major droughts occur, on average, around every 20 years. This is true for much of the central and western U.S. (Landsberg, 1982). A drought during the mid 1920s to mid 1930s was “possibly the most severe and longest of this century” (Moosburner and Williams, 1990). The droughts of the mid 1980s to mid 1990s, and the early 2000s, were also severe and, referring to how rapidly the level of Lake Tahoe dropped, may turn out to be even more severe than the 1920s–30s drought. The driest water year on record in Reno was 2000-01, and the driest two consecutive water years occurred in 1975-77. Table 5 lists some of the most severe droughts in the RenoCarson City-Lake Tahoe area during the last 100 years. In the past, there was nothing to lead to the conclusion that water would be the ultimate growth control. However, the tremendous and unexpected population growth in the arid Southwest has put water availability in the center spotlight for future planning. Education of the public, and EVAPORATION There is typically very little moisture in the lower atmosphere over western Nevada, and temperatures during the day can be quite high. As a result, water can evaporate from the surface of any area of standing water. This can be especially pronounced over large lakes in the dry desert areas of western Nevada. The rate of evaporation can be determined by using instruments, the most common of which is the evaporation pan. A Class-A evaporation pan (which is one of the most commonly used in the western United States) is about 4 feet in diameter and around 10 inches deep. Evaporation can occur at a faster rate over the water surface in an evaporation pan than it does over a large lake (Sellers, 1965). Lake evaporation is very difficult to measure directly. However, the rate from an evaporation pan can be calibrated to give a good approximation of evaporation from natural lakes and other bodies of water. During the winter, evaporation from lakes in western Nevada is negligible because the lake surface may be frozen or the temperature of the water surface may not exceed the dew point of the air above it. Because of this, evaporation is not measured from pans during the winter. However, from late spring through early fall the air temperature is high enough to cause evaporation from water surfaces. During a typical month in the summer only a quarter of an inch of rain may reach the surface, but during that same month a foot or more of water may evaporate into the atmosphere from a large lake in the high desert (Figure 21). Of the dozen or so evaporation pans located across western Nevada and the eastern Sierra two are in the RenoCarson City-Lake Tahoe region. Honey Lake, just across Table 5. Average annual precipitation in inches during drought (with percent of normal precipitation). Years Reno Tahoe City Central Sierra Snow Lab Average annual precipitation 1971–2000 7.48 32.66 64.68 Drought years (water years) 1924–35 6.29 (84%) 25.07 (77%) 37.58 (58%) 1946–49 4.95 (66%) 25.91 (79%) 45.13 (70%) 1976–79 5.91 (79%) 18.20 (58%) 46.44 (72%) 1987–94 5.77 (77%) 24.08 (74%) 50.37 (78%) 2001–04 5.21 (70%) 25.25 (77%) 51.57 (80%) Figure 21. Average pan evaporation totals at Honey Lake, California (1970–2004), and Lahontan Dam, Nevada (1948–1974). 40 so evaporation rates from it are somewhat lower than those at Lahontan Dam. These large evaporation rates certainly contribute to the water deficits seen across much of the western United States. Often the moisture is not made up until winter when large amounts of snow fall on mountainous regions. Even the large snowpack that results still may not make up for the water that was lost during the warmer months. Photo by John James the state line in California, is a station with one of the longest evaporation records. Honey Lake Fleming Fish and Game has been in operation for over 35 years. Pan evaporation at this location is right at 50 inches per year from April through October. The other location is at Lahontan Dam, between Reno and Fallon, Nevada. Pan evaporation there averages 68.59 inches per year. It should be noted that the pan at Honey Lake is in a partially irrigated area, Photo by John James Drought affects the Truckee River in downtown Reno, October 1991. Example of conditions during the drought of the late 1980s and early 1990s. Drought affects the upper Truckee River near Tahoe City in 1991. Example of conditions during the drought of the late 1980s and early 1990s. 41 Photo by Chris Ross Photo taken from Windy Hill in the late 1970s. Note the dust blowing across the eastern part of Truckee Meadows. Wind by Brian F. O’Hara Wind is common over western Nevada as anyone who lives in the region soon learns. Westerly winds over the region are caused by the strong afternoon heating experienced over the Great Basin during the summer. This heating causes pressure over western Nevada to be lower than over the adjacent Sierra Nevada. A “thermal trough” is thus formed over western Nevada. This difference in pressure generates winds that descend the eastern slopes of the Sierra (Hill, 1993). These winds are generally stronger near the base of the Sierra and decrease in speed as they move east through the Truckee Meadows and Washoe Valley. The diagrams in Figure 22 show the percentage of time the wind is from various directions for each month at Reno. There is a definite westerly component to the wind during the warm half of the year at Reno. This westerly wind is a common occurrence during summer afternoons in the valleys just east of the Sierra. Winds during the winter are generally from the south. This is due to the strong high pressure area that often forms over the Great Basin during the winter. Winds can come from any direction as synoptic -scale low pressure areas move through the region. Wind gusts associated with thunderstorms can also come from any direction. There is also a definite diurnal (daily) pattern to the wind. Figure 23 shows how the average wind speed changes throughout the day for each month throughout the year at Reno. During the winter the average afternoon wind speed does not differ much from the wind speeds recorded during the night. However, this changes during the late spring and summer. Wind speeds generally decrease during the night. But during the day, with the higher sun angle and relatively drier atmosphere, the air near the surface quickly warms during the morning and early afternoon. The rising air motions that are generated induce a corresponding increase in the horizontal winds at the surface. During the warmer half of the year, wind speed increases very quickly during the morning hours, and the wind is generally stronger during summer afternoons than it typically is during the winter (Figure 23). It is worth noting that Reno has one of the lowest average wind speeds in the nation (6.5 mph). Reno has a perception as a windy place due to the fact that the winds generally occur during the afternoon and evening hours, especially during the summer. WASHOE ZEPHYR As mentioned above, due to the strong heating which occurs over the Great Basin, winds during the summer tend to blow from the west during the afternoon (Hill, 1993). Depending on the strength of the high pressure area east of the region winds can become quite strong. This afternoon westerly wind has been dubbed the “Washoe Zephyr” and has probably been observed as long as the region has been settled. 42 Figure 22. Average wind speed and direction by months at the Reno/Tahoe International Airport (1949– 2003). The lengths of the radial bars represent the percentage of time the wind blows from each of the 16 directions. The width and shade of each segment of the bars indicate the wind speed, and the length of the segments indicates the percentage of time the wind blows at that speed from that direction. 43 Figure 22 continued. 44 Figure 23. Average daily variation in wind speed (miles per hour) at Reno, Nevada. 45 Figure 24. Formation process of mountain lee wave clouds. MOUNTAIN LEE WAVES A zephyr is a west wind (deriving its name from Zephyros, the Greek god of the west wind). The Washoe Zephyr descends the eastern slopes of the Carson Range and is strongest as it moves through Washoe Valley. In his book Roughing It, Mark Twain ([1872] 1995) described this strong wind as it moved through Carson City: Upper level winds are responsible for some of the most interesting cloud patterns seen over the western United States. One of these patterns is the mountain lee wave cloud. As the name implies, these clouds are formed downwind of large mountain ranges. The mountains disrupt the upper level wind flow, causing the air to undulate in an up and down pattern. As the air moves higher in the atmosphere it cools and its water vapor condenses into a cloud. Downwind of the wave crest the air is moving downward. This downward motion causes the air to compress and become warmer. As a result, the cloud evaporates. Even though the air is moving in a wavelike pattern downwind of the mountain range the only part of the pattern that is visible is the top of the wave where water vapor has condensed into a cloud. These waves do not move in relation to the mountains that are causing them so the resulting clouds do not move either (Wallington, 1966). These standing wave clouds, as they are called, can take many shapes, but they often have a lens shape with a rounded top and either a flat or a concave base. These lens-shaped clouds, called lenticular clouds, are common forms of mountain lee wave clouds. As the air rises downwind of the wave cloud a second wave cloud (or even a third or fourth) may form. A series of lee wave clouds can extend for 100 miles downwind of a large mountain range (Figure 24). Clouds may even form just above the mountain itself, in which case it is called a mountain wave (Scorer, 1972). Due to the high elevation of the Sierra Nevada, mountain lee wave clouds are occasionally seen downwind of it as shown in the cover photo and the photo on the next page. Conditions can be turbulent near the clouds themselves. The turbulence can even extend to the lower atmosphere, and rotor clouds can sometimes be seen below a lee But seriously a Washoe wind is by no means a trifling matter. It blows flimsy houses down, lifts shingle roofs occasionally, rolls up tin ones like sheet music, now and then blows a stage-coach over and spills the passengers; and tradition says the reason there are so many bald people there, is, that the wind blows the hair off their heads while they are looking skyward after their hats. Carson streets seldom look inactive on summer afternoons, because there are so many citizens skipping around their escaping hats, like chambermaids trying to head off a spider. Mark Twain, Roughing It In a study conducted during July and August 1998, Kingsmill (2000) found that the “valley stations all show a clear diurnal wind pattern in association with the Washoe Zephyr.” He found that at sites in Washoe Valley and around Carson City in Eagle Valley wind speed increased during late morning, but that the Washoe Zephyr started 2 to 4 hours later on sites to the north in the Truckee Meadows (Kingsmill, 2000). The Washoe Zephyr lasted longer in the Washoe Valley, ending 1 to 2 hours later than it ended in the Truckee Meadows. Another difference that Kingsmill found is that the Washoe Zephyr kept a generally westerly component in the Truckee Meadows but it came from a more southwesterly direction while in the Washoe, Eagle, and Carson Valleys. 46 Photo by Jack Hursh View to the south of downtown Reno and lenticular wave clouds. wave cloud (Powell and Klieforth, 2000). Pilots need to be cautious when flying near these clouds. Sailplane pilots, however, can use the lift generated by the upper level wind flow to achieve rapid ascents. They can remain aloft sometimes for hours by using the upwardly moving air near wave clouds to lift them again to higher altitudes. The area downwind of the Sierra near Minden, Nevada is a prime location for sailplane flights and many records have been set by pilots flying in this region. in the eastern foothills of the Sierra can reach nearly hurricane force. Wind speeds of over 40 mph with gusts to 80 mph or more have been reported at sites all along the foothills and valleys east of the Sierra during these strong wind events. Widespread damage can result with fences blown down, shingles taken from roofs, and vehicles (especially high-profile vehicles traveling along north-south roads) blown off the road. DUST STORMS AND SANDSTORMS SYNOPTIC-SCALE WIND EVENTS Dust storms and sandstorms are another danger from strong synoptic-scale winds. Many climatological factors contribute to the occurrence of dust storms. Landsberg (1966) stated that wind is the most important factor, because the “higher the wind velocity the more dust will be carried, provided it is available.” An arid landscape is necessary to provide this dust cover, and a period of below-normal precipitation can contribute to the dry conditions. A large area of fairly level ground is also necessary because “mountains will tend to break the force of the wind.” (Landsberg, 1966). Ground cover such as sagebrush is sparse over much of the western Great Basin and large areas of soil and sand are exposed to the elements. Areas of dust are also created when the water in shallow lakes evaporates. This alkali residue is easily picked up by strong winds and carried for miles. When this fine material becomes airborne it can reduce visibilities to less than a quarter of a mile. This can be especially dangerous to motorists who may not see cars stopped ahead of them. Some of the more intense sandstorms and dust storms can last two to three hours, but most are fairly short-lived, usually lasting no more than an hour. Some of the most damaging winds in western Nevada are not associated with strong thunderstorms. Large-scale winds (referred to in meteorology as synoptic-scale winds) are part of the general wind flow of the atmosphere. Winds at the surface of the Earth are affected by topography (ranging from hills to mountain ranges), trees, buildings, and obstacles that block the wind flow or change its direction or speed. However, above this friction layer, as it is called, the wind flow is generally uninterrupted and high wind speeds can be encountered just a couple of thousand feet above the ground. If the lower atmosphere is unstable (with warmer air near the surface and cooler air above it) the upper level winds are more likely to mix down to the surface (Whiteman, 2000). Across western Nevada this is more common during the colder half of the year when Pacific polar air masses invade the region. A common scenario is when cold air moves in from the northwest behind a cold front. The cold upper level air moves across the Sierra Nevada and this cold dense air then descends the eastern slopes of the Sierra. The air gains speed as it rushes down the mountainside and wind speeds 47 Photo by Mark Vollmer Lightning over the Carson Range, seen from the Tahoe Rim Trail, Mt. Rose Wilderness. Convective Weather by Brian F. O’Hara water vapor in the air condenses into clouds. The warmer the surface temperature, the faster and higher the air rises, and this can cause clouds to develop to very high levels. The tops of some of the more intense thunderstorms that develop from these clouds rise to over 40,000 feet above the surface (Figure 25). During the summer, thunderstorms are usually widely scattered so a particular location may not be affected by them very often. Even during the summer, Reno only reports thunderstorms an average of three days each month (Figure 26). Some locations are more conducive to thunderstorm development than others. The Sierra Nevada seems to be a preferred location for creating thunderstorms. Hill (1980) found that “on non-Zephyr days there is a marked preference for thunderstorms to develop over the Sierra Nevada. This is a reflection of the ability of these massive mountains to act as an effective elevated heat source.” On days when there is a Washoe Zephyr, Hill found that cumulonimbus clouds (from which thunderstorms form) did not form over the Sierra Nevada. The downslope winds associated with Although not as active as many areas east of the Continental Divide, western Nevada gets its share of convective weather. Afternoon thunderstorms can occur, mainly south of the Reno area. Destructive winds can be a hazard. These winds may be from a thunderstorm’s downdraft or from strong upper level winds that mix down to the surface. Due to the dry air mass typically over the region, hail is not a significant hazard, but does occur on occasion. Tornadoes are rare in Nevada, with the state averaging only about one (generally weak) tornado per year. However, like any tornado, when they do occur they can cause damage. Lightning is another hazard that affects the public more than most other thunderstorm-related hazards combined. THUNDERSTORMS Thunderstorms are fairly common across western Nevada during the warmer half of the year. Even during winter thunderstorms can occur if the air aloft is cold enough. However, they are usually experienced from May through September. The intense afternoon heating that occurs over the region causes air to rise. This rising air cools and the 48 the Washoe Zephyr apparently inhibited the upslope winds necessary to promote cumulonimbus development over the Sierra crest (Hill, 1980). Hill also found that, on days during which a Washoe Zephyr occurred, thunderstorm development was more common over the Pine Nut Mountains. The westerly winds associated with the Zephyr may contribute to the upslope winds in the Pine Nut Mountains, helping thunderstorms to form. THUNDERSTORM WIND GUSTS Downdrafts from thunderstorms can exceed 50 mph, strong enough to cause damage to structures. Trees can also be damaged and even uprooted. A thunderstorm wind gust might last ten minutes or less, a much shorter time than a synoptic-scale wind event, but, with wind gusts approaching 80 mph, widespread damage could occur during that relatively short time . Most of western Nevada is sparsely populated and most areas would not be damaged by thunderstorm downdrafts, except for a few uprooted trees. However, if a strong thunderstorm occurred over a populated area such as the Reno/Sparks metropolitan area or Carson City there would be a greater chance that wind damage could result. DRY MICROBURSTS It is not necessary to have a thunderstorm in order to have strong damaging winds. Strong downdrafts can be generated below high-based clouds that are common across the Great Basin during the summer. In the warm dry air mass typically over the region during the summer, cloud bases are often over 10,000 feet above the ground, and they may even be above the mountain tops (approaching 15,000 feet). Any rainfall that is generated in the cloud falls through this very deep dry air mass. Rain evaporates as it falls through dry air. This process of evaporation cools the air. As more raindrops evaporate the air continues to cool. This cool air quickly becomes denser than the warmer air surrounding it and rushes to the ground as a strong downdraft or downburst. When the downdraft reaches the ground it spreads in all directions if Figure 25. The development of a thunderstorm from the cumulus stage (all updrafts within the storm) through the mature stage (both updrafts and downdrafts) to the dissipating stage (all downdrafts). Figure 26. Average number of days with thunderstorms at Reno, Nevada (1943–2004). 49 Photo by Kris Ann Pizarro the air has fallen straight down. If the downdraft air hits the ground at an angle it will tend to move in the general direction it was traveling when it reached the surface. If the outflow wind from a downburst extends more than 2.5 miles from its point of contact with the ground it is classified as a macroburst. If the wind outflow extends 2.5 miles or less from its origin it is called a microburst (Fujita, 1985). If measurable rain is recorded with the microburst it is called a wet microburst. However, over the dry Great Basin, very little rainfall reaches the ground. Microbursts over western Nevada are usually dry microbursts. However, microbursts are not confined just to dry areas of western Nevada. On September 13, 1987, a microburst occurred over Lake Tahoe. As described in the publication Storm Data, a “microburst from dissipating thunderstorms in the Zephyr Cove area of Lake Tahoe estimated at 60 to 70 mph damaged a few sailboats.” (USDC, 1987). Wind speeds in dry microbursts can reach speeds similar to those in thunderstorm downdrafts. Damage can result as wind speeds of well over 50 mph travel across the area. However, damage patterns are different than those caused by tornadoes. A tornado creates a fairly narrow damage path with evidence of rotation evident across the ground. Damage patterns from microbursts have a radial pattern as the straight-line winds move away from the point of contact with the ground. Evidence of these straight-line winds can be seen as trees and other objects are all blown down in the same direction. HAIL Large hail is not common in western Nevada. Flora (1956) stated that in “twenty-five years the only Nevada loss of consequence reported to the Weather Bureau was $39,000, caused by a hailstorm on July 21, 1943, in Fernley and the surrounding area.” It is probable that hail forms in many of the thunderstorms that occur over Nevada, especially the stronger storms. However, large supercell thunderstorms (which would generate the largest hailstones) do not often form over the Great Basin due to the lack of moisture over the region. Also, because of the hot, dry ground across the Great Basin, clouds that form tend to have high bases, sometimes over 10,000 feet above the surface. Hailstones that do form in thunderstorms tend to melt as they fall through the dry air mass below the cloud base. Only the largest hailstones would not completely melt before reaching the ground. This is why hailstones that reach the ground in western Nevada are relatively small, usually less than an inch in diameter, and often much smaller than onehalf inch in diameter. There have been more reports of hail in western Nevada during the late 1980s and 1990s. This is probably due to increased efforts of National Weather Service personnel in soliciting and verifying reports of not just hail but any occurrence of severe weather. Since the early 1960s, 26 hail events across the region were reported in the publication Storm Data (USDC, 1959–2005). Dust devil. TORNADOES Tornadoes are rare in Nevada, which averages about one tornado a year and these tornadoes are usually weak. From a review of Storm Data, since the early 1960s only 12 tornadoes have been reported in extreme western Nevada (USDC, 1959–2005). However, due to the sparse population in the rural areas it is probable that many more tornadoes have occurred, although, with the lack of supercell thunderstorms climatologically, these tornadoes most likely would have been relatively weak (F0 or F1 in intensity). According to newspaper accounts a tornado was also reported in Reno on April 1, 1949. Unlike tornadoes, waterspouts do not form from cumulonimbus (thunderstorm) clouds. Waterspouts form from cumulus clouds, and they are weaker than tornadoes. However, they can occur over larger lakes such as Lake Tahoe and Pyramid Lake, mainly during the summer, and can damage boats that venture too close to them. 50 reported in Storm Data, a dust devil in Gardnerville, Nevada on April 21, 1997 “lifted a 3 year old child a half foot off the ground and knocked over a swing set.” (USDC, 1997). FUNNEL CLOUDS A tornadic circulation that does not reach the ground is called a funnel cloud. These are generally short-lived, and most of the funnel clouds observed in the eastern Sierra and western Nevada generally last five minutes or less before ascending back into the cloud base. LIGHTNING Lightning is associated with thunderstorms. In fact, thunder is the sound produced by the expansion of the rapidly heated air around a lightning bolt (Uman, 2001). Lightning should always be considered dangerous, and anyone who sees lightning or hears thunder should seek shelter until the thunderstorm has passed. Lightning bolts can extend up to 10 miles from their parent thunderstorm. So, even if a storm appears to be far away, it may still be close enough to be dangerous. Lightning can cause damage to buildings and can start fires in many types of vegetation. People can be injured or killed if they are struck by lightning. Livestock can also be struck and killed since they often are on open rangeland in the West. Lightning occurs many times during the summer thunderstorm season in western Nevada. Since the early 1960s, the publication Storm Data has listed 15 incidents in which lightning caused damage or injured people in the Reno-Carson City-Lake Tahoe region, but, no deaths were reported with these events. Most of these events, as might be expected, occurred during the late afternoon and evening when thunderstorms are most common across the area. DUST DEVILS Photo by Mark Vollmer Dust devils are sometimes mistaken for tornadoes but they are quite different. While tornadoes form as a result of strong rotating winds inside of cumulonimbus clouds, dust devils form at ground level as a result of strong surface heating. The circulation that forms at ground level then develops upward (Flora, 1953). In western Nevada, dust devils occur mainly during summer afternoons. Ground that is bare or has very little vegetation can heat rapidly during the day. Even if the air temperature at observation level (around 5 feet) is in the 90s, the temperature at ground level can be even higher. This very warm air at ground level, being less dense than the cooler air above it, moves upward and cooler adjacent air at ground level flows in to replace it. The circulation that develops can reach 1000 feet or higher. Dust devils are never as strong as tornadoes, but they can cause slight damage by knocking over lawn furniture or trash cans. As Evening thunderstorm over distant Pine Nut Mountains. View across Washoe Valley and the Virginia Range from the Mt. Rose Highway. Lights of Washoe City can be seen in the near distance. 51 Photo by Jeremy Vlcan Waterfall fire. View toward Lakeview Hill from about halfway through Washoe Valley, July 2004. Wildfires by Brian F. O’Hara Because of the dry air mass over the high desert of the Great Basin, thunderstorms typically produce very little rainfall that reaches the ground. Thus these thunderstorms are referred to as dry thunderstorms, and usually occur during the warmer half of the year. Lightning strikes from these thunderstorms occasionally start wildfires, but some wildfires are caused by human carelessness. Davis (1959) states that outbreaks “of forest fires, both in size and number, tend to occur with hot weather or in periods when the prevailing temperatures are above normal.” The fire season in western Nevada and the Lake Tahoe region generally runs from mid May to mid October. During the spring and early summer natural vegetation dries out and, by May or June, plants such as grasses and sagebrush may contain very little moisture. As a result, the fire danger associated with these plants is very high. A fire can easily start if a lightning bolt strikes dry plants such as these. Thunderstorms during the fire season are often caused by monsoon moisture that moves into the region from the south, and also by low pressure systems over the region. The air mass over the region during the summer tends to be hot and dry with significant low-level instability (Schroeder and Buck, 1970). Prolonged drought can increase the possibility of fires growing large “because drought dramatically decreases the moisture content of both live and dead fuels (Whiteman, 2000). Due to the dryness of the vegetation the resulting fire can spread rapidly. If this occurs near a populated area it becomes critical that the fire is extinguished as quickly as possible. This was true during the Waterfall Fire, which burned over 7500 acres near Carson City in July 2004. Many homes and outbuildings were destroyed, but the fire was kept out of Carson City itself. The Washoe Zephyr winds that occur during the afternoon can drive a fire and make it grow rapidly. However, any strong wind can help to drive fires out of control. A fire in Reno on March 2, 1879 destroyed many buildings and left hundreds of people homeless. It apparently started from a burning stove pipe which set a pile of wood on fire. The Reno Weekly Gazette (March 6, 1879) reported that the “wind was blowing hard from the southwest and fanned the spark into instant conflagration.” Most of the buildings in the city were made of wood so the fire had plenty of fuel to feed on as it moved east. The newspaper reported that 50 acres of businesses were destroyed. 52 Perhaps the worst fire in the region’s history was the one that destroyed Virginia City on October 26, 1875. Most of Nevada’s then-largest city was burned to the ground, extending from the Comstock mines in the north to the south edge of town, and from Washington Street in the west to the east edge of town. The wooden buildings were tinder dry and ignited instantly. Strong wind “set the disaster in motion when it carried the flames to roofs downhill” (James, 1998). The Virginia City Territorial Enterprise (October 27, 1875) reported that the fire started in a lodging house on A Street. The paper went on to say that a “breath of hell melted the main portion of the town to ruins” (James, 1998). Not only wooden structures, but brick buildings were destroyed. Scores of buildings (with their entire contents) were burned. Total damage was estimated at between $5 million and $10 million (in 1875 dollars) (Elliott, 1987). Like the Waterfall Fire, another wildfire threatened Carson City, this time from the south. On September 28, 1926, a wildfire started in Clear Creek Canyon, west of Stewart, Nevada, south of Carson City. The Reno Evening Gazette (September 28, 1926) stated that, because of an early morning breeze, the fire “rushed up [Clear Creek] canyon, crossed the road at Swift’s station and then the wind changed and became stronger and scattered the flames in all directions.” The wind forced the fire toward Lake Tahoe and Carson City, and smoke from the fire could be seen in Reno. The fire continued into the next day before it was contained. Tragically, five men died while fighting the fire when they were trapped in Clear Creek Canyon and could not escape the flames. In late August 1960 the Donner Ridge Fire affected the region. As a result of this fire, Reno was without electricity for four days. During 1973 many fires raged from the Reno-Sparks area, to just east of Placerville, California, and Table 6. Major wildfires in the Reno-Carson City-Lake Tahoe Area (1999–2005). south to Gardnerville. Fires during September 1981 burned much of the Lightning (L) Date under Location Acreage eastern slope of the Carson Range Name of fire or Human control (county/counties) burned above Washoe Valley, and near the (H) caused Mt. Rose Highway in the Whites Fish Complex Aug 29, 1999 Washoe 47,633 L Creek-Galena Forest area. Reno Complex July 2, 2000 SW Washoe 18,080 L The erratic winds associated with many fires make them very Ramsey July 4, 2000 E Douglas 5,666 L difficult to bring under control. This Seneca July 11, 2000 SW Washoe 1,110 H is why it is extremely important that there is defensible space around Cold Springs July 25, 2000 SW Washoe 400 H houses and other buildings. Residents Red Rock Aug 3, 2000 SW Washoe 2,203 L can make their properties more fire resistant by reducing the amount of Arrow Creek Aug 4, 2000 SW Washoe 2,900 L vegetation next to their homes. The Sutcliffe Aug 4, 2000 S Washoe 300 L use of decorative rock and other forms of xeriscaping can help to Right Hand Aug 14, 2000 S Washoe 452 L reduce the amount of flammable Siegel May 15, 2001 E Douglas 800 L material near buildings. Some of the Warrior May 30, 2001 SE Washoe 6,508 L largest fires in the Reno-Carson CityLake Tahoe region from 1999 E Nevada and SW Martis July 1, 2001 14,500 H through 2005 are listed in Table 6. Washoe Pleasant Valley Aug 11, 2001 SW Washoe 775 L Antelope Aug 11, 2001 S Washoe 900 L Fish Aug 15, 2001 SE Lassen and W Washoe 21,343 L Cannon June 28, 2002 Douglas and Mono 22,750 H Gondola July 6, 2002 E El Dorado 670 H Highway 50 June18, 2003 SW Washoe 575 H Robb July16, 2003 SW Washoe 2,196 H Waterfall July 20, 2004 Carson City SW Washoe 8,700 H 53 Floods by Gary Barbato Winter rain and snow in the eastern Sierra Nevada provide the region with almost all of its streamflow, as well as its reliable water supply. Runoff from steady spring and early summer snowmelt is stored in Lake Tahoe and the many other lakes and reservoirs throughout the Sierra and western Nevada so that residents of the region have a sufficient water supply during the summer dry season. Although strong thunderstorms with heavy rainfall can develop during the summer, warm season precipitation is typically light, spotty, and, compared to winter precipitation, rare. Summer drought is common and expected throughout northern California and western Nevada. The heaviest winter precipitation falls in the region during what is sometimes called a "Pineapple Express" or "Pineapple Connection." How this scenario typically develops is diagrammed in Figure 27. About a week to 10 days before the heavy precipitation occurs on the west coast of the United States, heavy rain is occurring over the far western tropical Pacific, and a moisture plume from this precipitation begins to extend northeast. There is a strong polar jet moving clockwise around high pressure over the Gulf of Alaska. By about three to five days before the heavy precipitation, the heavy rain in the tropical Pacific has moved east, and the moisture plume now extends farther northeast toward the west coast. The high pressure over the Gulf of Alaska has weakened and moved westward, and is now centered over the Aleutian Islands. A low pressure trough has begun to develop over the eastern Gulf of Alaska, and the jet stream has split into two equally strong branches. One branch continues to move clockwise over the Aleutian High, but a southern branch of the jet stream is now set up south of the high pressure area and the low pressure trough over the Gulf of Alaska, and is in position to push the moist air directly into the west coast of the United States. By the time the heavy precipitation arrives at the west coast, the trough of low pressure over the northeastern Pacific Ocean (now called the “Aleutian Low”) has become large, deep and strong. The stream of warm, moist, unstable subtropical air extends from Hawaii all the way to just south of the Aleutian Low. Cool moist air from the Gulf of Alaska causes a series of fronts to move out of the Aleutian Low toward the California coast, which can then cause prolonged heavy precipitation in the region. Figure 27. Typical wintertime weather patterns preceding west coast heavy precipitation events. Map courtesy of the NOAA Climate Prediction Center. 54 Rain-on-snow type flooding is characterized by sharp rises and high peak flows, usually with slow recessions. Flooding may occur on all rivers originating in the eastern Sierra at the same time, although the magnitude of flow can vary greatly from one river to another, depending on the location, elevation, temperature (or snow level) and intensity of the precipitation. The travel time of a flood wave from the headwaters to the valley areas can range from just 3 or 4 hours on the Susan River, to 6 to 10 hours on the Truckee (from Tahoe City to Reno), to about 24 hours on the Carson River (from headwaters upstream of Markleeville and Woodfords, California to Carson City), to about 2 to 3 days from the headwaters of the Walker River (above Bridgeport and Coleville, California) to the Mason Valley (Yerington, Nevada) area. The flood wave on the Walker may take over a week to travel down from the headwaters to Walker Lake. Walker River flood crests dissipate significantly below Bridgeport and Topaz Lakes as they traverse the broad Mason Valley. Even though flooding in the headwater areas usually results in valley flooding, this is not always the case, especially if there are only isolated areas of heavy precipitation, or if most of the precipitation does not make it very far over the Sierra crest. In December 1964, January 1969, January 1970, March 1971, January 1980, and February 1982, flooding was much worse in the headwater areas than in the valleys, which, in many of these cases, had only minor flooding . When Pacific storms do make it over the Sierra crest and snow levels are below about 7000 feet, flooding can be much worse in the valley areas than in the headwaters because: (1) there is no runoff in the headwaters because it is snowing; and/or (2) a large snowpack at the higher elevations soaks up much of the rainfall; and (3) a large low elevation snowpack melts, adding to runoff in the lower elevations. These three scenarios result in little runoff from the headwater areas, but there can be tremendous amounts of runoff from the lower portions of the basins. The February 1986 and December 2005 floods were good examples of this, with much of the flooding occurring on lower tributaries of the mainstem rivers. Prolonged minor to moderate flooding over a large area may be caused by a rapidly melting large snowpack in spring and early summer on rivers and streams without large reservoirs in the headwaters. This would include the Carson River above Lahontan Reservoir and the West and mainstem Walker Rivers. Snowmelt floods are not considered a problem on the Truckee River through the Truckee Meadows due to upstream reservoir regulation. Snowmelt floods are largest during years with extremely large (greater than 150% of average on April 1) mid- to highelevation snowpack water equivalent, and occur during a rapid warm up, usually from mid April to mid June, or even as late as early- to mid July on the Walker River basin. Snowmelt floods have extremely large volumes and may last for many days or even weeks as the snow melts, but the flood crests and resulting damages are far less than the rain-on-snow floods which can occur during the winter. Also, these types of floods are far easier to forecast than rain-caused floods because they are driven by warm temperatures. The Sierra Nevada has a major effect on the hydrology of western Nevada. This mountain range effectively blocks most precipitation from reaching areas to the east. Western Nevada is in the rain shadow of the Sierra, and most of the precipitation occurs west of the crest. Significant precipitation does get into the Lake Tahoe basin and the higher elevations on the east sides of the Sierra Nevada and the Carson Range, but only a small percentage makes it into the lower elevations of western Nevada. So, the large, usually reliable snowpack and reservoirs in the eastern Sierra Nevada are able to supply dry western Nevada with most of its water supply. Huge amounts of snow can fall in the upper reaches of the eastern Sierra Nevada. Snow depths of over 10 feet are common at the higher elevations, though depths of over 25 feet are relatively rare. At Donner Summit (elevation 7239) on the crest of the Sierra Nevada, snowpack depths equaled or exceeded 25 feet only six times since records began in 1879 (1879–80, 1889–90, 1894–95, 1906–07, 1910–11, and 1951–52). The maximum depths were recorded during the winters of 1879–80 and 1889–90, when over 31 feet was on the ground. Total snowfall has exceeded 60 feet at Donner Summit during the winters of 1879–80, 1889–90, 1937–38, and 1951–52. The winter of 1937–38 had the largest snowfall, with over 68 feet (819 inches) recorded (Osterhuber, 2001). However, snow depth at Donner Summit is not always a foolproof way to measure total annual precipitation because during many winters much of the precipitation may fall as rain. RIVER FLOODS Western Nevada and the eastern Sierra Nevada have a long history of infrequent, but very damaging river flooding, with accounts dating back to December 1852. Mainstem river flooding has occurred only between the months of November and May. Although summer thunderstorms can cause heavy precipitation and isolated flash flooding on creeks and streams during the summer, the total amount of runoff is insufficient to bring rivers to flood stage. The largest regional floods occur between November and March and are usually caused by prolonged warm, heavy rain falling on a large snowpack or frozen or saturated ground during the winter. However, having a large snowpack is not a prerequisite for flooding during an intense, prolonged, warm winter storm. These storms can produce massive amounts of precipitation which can lead to flooding without much of a snowpack over the region, especially if soils are saturated due to a wet autumn. Nevertheless, heavy rainfall on a significant snowpack at all elevations, from the western Nevada valleys up to the higher elevations of the Sierra, often leads to the most serious flooding. Generally, a foot of snow at the 5000-foot elevation in the eastern foothills of the Sierra would be considered significant; at higher elevations, over 120% of average snowpack water equivalent is significant. All of the region’s largest floods have resulted from a prolonged warm rain-on-snow weather pattern. 55 (1996, 1997a, 1997b, 1997c); Osterhuber (1993, 2001); U.S. Army Corps of Engineers (USACE) publications, data, and correspondence (1970, 1972, 1974, 1980, 1983, 1997); U.S. Department of Commerce (USDC) (1997); U.S. Geological Survey (USGS) publications (1954, 1958, 1960, 1982, 1991); USGS Fact Sheets (FS-077-97, FS-12397, FS-183-97, FS-005-98); and correspondence (R.E. Bostic, personal communication, 2007; R.A. Hunrichs, personal communication, 2007). Much of the information about the January 1997 flood was obtained by NWS Reno office staff after the flood (Barbato and Hickman, 1997). The historical information about these past floods was derived by the above authors from such sources as available streamflow records, newspaper files, historical documents, interviews with local residents, and from photographs of these past floods. LARGEST HISTORICAL FLOODS IN WESTERN NEVADA AND THE EASTERN SIERRA NEVADA Despite the fact that western Nevada is very dry and is in the rain shadow of the Sierra Nevada, major river floods have occurred here and in the eastern Sierra, although they are not frequent. The fact that they are infrequent sometimes causes the area’s population to forget their significance and danger in the long periods between major floods. This has led to disastrous results in the past, as residents continue to build in the floodplains of the rivers and streams during the long periods between major floods. Table 7 lists the largest floods of record in the eastern Sierra and western Nevada. Following are descriptions of some of the major raininduced floods that have occurred along the Truckee, Carson, and Walker Rivers since the first EuropeanAmerican settlers began arriving in the 1850s. Most of the flood information in this section was obtained from excellent accounts put together by Rigby and others (1998); Altine and Dunn (1997); the USDA Nevada River Basin Survey Staff (1969); Goodwin (1977a, 1977b); Horton December 24–30, 1852. The earliest record of flooding in western Nevada was made by the settlers of Genoa in Carson Valley, Nevada’s first European-American settlement. Beginning about Christmas Eve, heavy snow fell in the Carson Valley for two days and piled up to 3 feet deep on the valley floor. This was followed by four days of warm rain, melting all of the snow, and inundating the Carson Valley by December 30. The flooding was extensive, but damage was minor as Third highest flow the population was well away from cfs (date) the low areas of the valley. Nothing is known about flooding in other portions of western Nevada at this time, due to the lack of population 2,740 (3/8/1986) (Rigby and others, 1998). Based on the limited description of the magnitude of flooding, it was probably 7,760 (12/23/1955) greater than a 50-year flood on the Carson River. Table 7. Largest floods of record. Station Highest flow Second highest flow cfs (date) cfs (date) Lake Tahoe and Upper Truckee River basins Upper Truckee R. at S. Lake Tahoe 5,480 (1/2/1997) 2,850 (12/31/2005) Truckee River basin Truckee 11,900 (1/2/1997) 11,000 (2/1/1963) Farad 17,500 (11/21/1950) 15,500 (12/11/1937) 15,300 (3/18/1907) Reno 20,800 (12/23/1955) 19,900 (11/21/1950) 18,800 (3/26/1928) 2,090 (1/1/1997) 1,000 (1/31/1963) Steamboat Creek 3,600 (2/17/1986) 3,600 (12/31/2005) Vista 18,900 (2/1/1963) 18,500 (1/2/1997) 16,100 (2/18/1986) Wadsworth (below Derby Dam) 19,700 (1/3/1997) 18,400 (2/1/1963) 16,900 (2/19/1986) Gardnerville 20,300 (1/3/1997) 17,600 (12/23/1955) Woodfords 8,100 (1/1/1997) Carson City 30,500 (1/3/1997) 30,000 (12/24/1955) 21,900 (2/1/1963) Ft. Churchill 22,300 (1/3/1997) 20,000 (3/19/1907) 16,600 (2/19/1986) 6,220 (11/20/1950) 5,800 (12/11/1937) Carson River basin 13,400 (2/1/1963) 4,890 (2/1/1963) 4,810 (12/23/1955) West Walker River basin Coleville 12,300 (1/2/1997) 56 December 20, 1861–January 2, 1862. Up to 2 feet of heavy, wet snow fell on the valley floors the week before Christmas, 1861. This was followed by a period of extremely cold weather, which turned the wet snow into sheets of ice. From Christmas Day to December 27, heavy, warm rain fell and eventually melted the icy snow, causing extensive flooding. The Carson Valley became a lake, but luckily very few of the people living there at the time were located near the river, and little damage was reported. In both Empire (east of Carson City) and Dayton (the third largest town in Nevada Territory at the time), drownings were reported and buildings were washed away (Rigby and others, 1998; and Goodwin, 1977a). Just above Dayton, the Island Stamp 57 Photo courtesy of the Nevada Historical Society Mill floated off its foundation. Two people drowned trying to escape. The bridge over the Carson at Dayton was destroyed, and floodwaters reached well up into the town (Goodwin, 1977a). This was the earliest damaging flood on record in the Truckee Meadows. Along the Truckee River, all settlements were either destroyed or flooded, and the Truckee Meadows became a huge lake. All bridges over the Truckee from Verdi to Glendale (in present-day Sparks, near where Steamboat Creek enters the Truckee) were destroyed. This included the bridge built by Charles Fuller in 1859 at the future site of the Virginia Street bridge in Reno. No measurements were available, but based on the description of the Flood waters at Virginia Street bridge in Reno during flood on March 18, 1907. flood it was probably between a 50and a 100-year flood event on both the Carson and Truckee Severe flooding occurred on the Truckee and Carson river basins. Rivers, though flooding was not as damaging on the Walker River. The flooding was caused by heavy rain December 20, 1867–January 3, 1868. This flood again falling on a fresh, heavy late season snow cover which turned the Carson Valley and Truckee Meadows into huge extended to the valley floors (Rigby and others, 1998), as lakes, exceeding the flood crest set in December 1861well as on frozen or saturated ground (Horton, 1997b). The January 1862, as well as the amount of damage, as more runoff combined with snowmelt and the Truckee, Carson, people were in the region by this time due to the Comstock and Walker Rivers quickly rose. mines. It was caused by two prolonged, unseasonably Many square miles of the Truckee Meadows were warm rain-on-snow events in the Sierra Nevada which flooded by the Truckee River, from Vista west to Sparks, occurred from December 20, 1867 to Christmas Day, 1867, and south along Steamboat Creek beyond Boynton Slough. and from December 30, 1867 to January 2, 1868. All The entire community of Glendale was evacuated during bridges in the Carson Valley were swept away, including the flood (Goodwin, 1977b; USACE, 1970). The Virginia William Cradlebaugh’s toll bridge, the first bridge over the mainstem Carson River in Carson Valley. In the Truckee and Truckee Railroad bridge over Galena Creek in Pleasant Meadows, both Glendale (east of present-day Sparks) and Valley was washed out, and the Electric Light Bridge near Lake’s Crossing (now Reno) were flooded and the bridges Booth Street and several other bridges in Reno were in those towns were destroyed. This flood caused the severely damaged (Rigby and others, 1998). South of the Central Pacific Railroad to select Lake’s Crossing as their Truckee River, the Truckee Meadows flooded from the Truckee Meadows station site instead of (at the time) the Virginia Range foothills westward to the Huffaker Hills. A much larger Glendale (Goodwin, 1977b). No measurements 16-year old boy attempting to rescue a person from a tree were available, but based on the description of damages, it on an island was drowned when his boat overturned could have been as great as a 100-year flood. (USACE, 1970). The 1907 flood ranks as the last recorded flood that March 16–23, 1907. This was the early “benchmark” raincaused severe damage along the entire length of the Caron-snow flood in western Nevada, against which all those son, from its headwaters above the Carson Valley downcoming later in the twentieth century would be compared. stream to the former Churchill County seat of Stillwater, It is the first major flood in the region for which there are just west of Stillwater Marsh. This was because Lahontan some streamflow records, and ranks at least equally with Dam was not completed until 1915. Fallon was established the two great nineteenth-century floods in 1861–62 and in 1896, and parts of the town were severely flooded for 1867–68 (Goodwin, 1977b). Instantaneous flow records do the first and only time in its history, because Lahontan not exist for the Truckee River at Reno for this flood. Dam was not yet protecting it (Goodwin, 1977a). “Every However, if the estimate by the USACE of the peak flow bridge on the Carson (River), from the Sierra Nevada to the for this flood at Reno is believed, it ranks as the fourth Humboldt-Carson Sink was destroyed during the 1907 largest flood of record on the Truckee River at Reno. It was flood” (Goodwin, 1977a). This included the Virginia & estimated by the U.S. Department of Agriculture, Natural Resources Conservation Service that "under similar condiTruckee Railroad bridge and the McTarnahan Bridge, both tions of settlement and development, this flood event most of which connected Carson City with Minden, and both of likely would have at least equaled the devastating floods of which had just been completed a few months before the 1950 and 1955 and exceeded the recorded damage of the flood. The Cradlebaugh Bridge, located near where the flood of December 1937." (Horton, 1997b). present U.S. Highway 395 bridge crosses the Carson River, March 23–28, 1928. The Truckee River was most affected by this flood, which is estimated to have been about as severe as the March 1907 flood at Reno, and ties for the third worst flood on record there. However, flooding on the Carson River was not nearly as severe as in the 1907 flood. When this storm began on the 23rd as a snowstorm, it was hailed as a “drouth-breaker” because the winter season had, up until late March, been dry. By March 25, residents in the lower Truckee Meadows along the river were evacuating due to severe flooding Truckee River flooding, Reno; March 1928. (Goodwin, 1977b). Several thousand Chestnut Street (now Arlington Avenue) bridge was acres of lowlands along the Truckee River were flooded, damaged to such an extent that it had to be replaced. Log especially from Sparks downstream to Vista. The Truckee jams and debris deposited on the upstream sides of bridges Meadows “Lake” grew to “a better than seven-mile arc at had to be broken up by blasting. Ranching areas were the western base of the Virginia Range” by March 27 hardest hit, with the loss of livestock and pasture. About (Goodwin, 1977b). Residents and livestock along the river 500 people in the Reno-Sparks area were made homeless were evacuated, as roads, bridges, and homes were subby the flood (USACE, 1970). Table 10 lists flood flow data merged. A few refused to evacuate, and they later had to be for the December 1937 flood. rescued by boat. One and a half miles of the newly comNovember 13– 23, 1950. Flooding during mid November pleted U.S. Highway 40 between Sparks and Vista were 1950 caused widespread damage on the Truckee, Carson, submerged to a depth of one foot. As reported by Goodwin and Walker Basins, and was the largest flood in the region (1977b) “the Truckee went on a rampage through Reno and since streamflow records began (USACE 1970). The flooding the Truckee Meadows, which was unequaled since 1907.” was caused by “a sequence of rapidly moving storms and Table 9 lists flood flow data for the March 1928 flood. unseasonably high temperatures that melted most of the December 9–14, 1937. Warm rain falling from the evening early snowpack in the Sierra Nevada.” (Rigby and others, of the 9th through the evening of the 11th melted much of 1998). Like previous rain-on-snow events, snow levels the mountain snowpack. The Truckee, Carson, and Walker averaged between 8000 to more than 10,000 feet during th Rivers were out of their banks by the 11 (Goodwin, much of the precipitation period. Adding to the problem 1977b). Downtown Reno was flooded by the Truckee was that soils were extremely wet before the November th River on the 11 and the Truckee Meadows became a vast storms, due to 300 percent of normal precipitation throughlake from near what is now the U.S. Highway 395 Bridge out the area in September and October 1950 (USGS, 1954). near the Grand Sierra Resort (formerly Reno Hilton) east to the Glendale/Vista area, and south along Steamboat Creek Table 9. March 1928 flood flow data. through December 14 (Rigby and others, 1998). The Station Table 8. March 1907 flood flow data. Station Date Peak or Average Daily Flow (cfs) Event Magnitude Date Event Magnitude Truckee River basin Truckee River basin Farad 3/25/1928 12,000 35-year Reno 3/26/1928 18,800 40-year 3/28/1928 12,000 15-year 3/26/1928 2,570 2-year Ft. Churchill 3/28/1928 2,710 2-year Farad 3/18/1907 15,300 70-year Wadsworth Reno 3/18/1907 18,500 40-year (below Derby Dam) Vista 3/18/1907 10,000 10-year Carson River basin 20,000 175-year Carson River basin Ft. Churchill 3/19/1907 Peak or Average Daily Flow (cfs) Gardnerville 58 Photo courtesy of the Nevada Historical Society was washed away despite the fact that it had been rebuilt and strengthened after it had been washed away in 1890. The Southern Pacific Railroad bridge just west of Fallon also was destroyed. Table 8 lists flood flow data for the March 1907 flood. Station Table 10. December 1937 flood flow data. Station Date Peak or Average Daily Flow (cfs) Event Magnitude Date Peak or Average Daily Flow (cfs) Event Magnitude Truckee River basin Truckee River basin Truckee 11/20/1950 6,480 20-year Farad 11/21/1950 17,500 100-year Farad 12/11/1937 15,500 70-year Reno 11/21/1950 19,900 50-year Reno 12/11/1937 17,000 35-year Vista 11/21/1950 8,750 10-year Vista 12/12/1937 9,760 10-year 11/22/1950 9,180 8-year Wadsworth (below Derby Dam) 12/13/1937 8,970 Wadsworth (below Derby Dam) 8-year Carson River basin Carson River basin Gardnerville 11/21/1950 12,100 35-year 11/20/1950 4,730 60-year Gardnerville 12/11/1937 10,300 25-year Woodfords Woodfords 12/11/1937 3,500 30-year Carson City 11/22/1950 15,500 25-year Ft. Churchill 12/14/1937 5,500 8-year Ft. Churchill 11/23/1950 7,850 15-year 6,220 40-year Walker River basin Walker River basin Coleville 12/11/1937 5,800 Coleville 30-year 59 11/20/1950 Photo courtesy of the Nevada Historical Society Total damages on the Truckee, Carson, and Walker basins were $4.4 million ($37.5 million in 2007 dollars). Of this amount, $1.98 million ($16.9 million in 2007 dollars) was in the city of Reno (Rigby and others, 1998; USACE, 1970; and USGS, 1954). Over 41,000 acres were flooded on the Truckee, Carson, and Walker Basins, with 33,000 acres of this total in the Carson River basin (USGS, 1954). Two deaths were reported, and the American Red Cross assisted about 200 persons who were evacuated from their homes (Rigby and others, 1998), and at least 15 families were left completely homeless (USGS, 1954). Two men and two patrolmen on duty were reported to have been carried off U.S. Highway 40 (now Interstate 80) and down a steep embankment by a slide in the Truckee Canyon (USGS, 1954), and U.S. Highway 40 in the Truckee Floodwaters covering the Sierra Street bridge in Reno during the November Canyon was closed for more than a 1950 flood. week after the flood. Residents of Floriston in the Truckee Canyon were isolated except for a In the Truckee River basin, floodwater covered much footbridge when the bridge crossing the river was washed of downtown Reno, and extended from West Second Street out. Also destroyed were several sections of U.S. Highway on the north to Mill Street on the south (USACE, 1970), 395 in the West Walker Canyon south of Coleville (USGS and was 4 feet deep on the main floor of the Riverside 1954). At least six bridges on County or State secondary Hotel (Rigby and others, 1998; USACE, 1970). All bridges routes in the Gardnerville-Markleeville-Coleville area were across the Truckee were closed, and the Rock Street Bridge washed out and others were in danger of failing (USGS, was destroyed. Water was 3 feet deep in much of down1954). Lake Tahoe rose an amazing 1.89 feet from Novemtown Reno, with velocities high enough to move parked ber 13 through December 6, an increase of about 193 cars, and several were tipped over by the raging currents square miles of lake surface, or 233,000 acre feet. Pyramid Lake rose 1.7 feet from November 15 through December Table 11. November 1950 flood flow data. 10 (USGS, 1954). Photo courtesy of the Nevada Historical Society (USGS, 1954). About 6,300 acres were flooded in the Truckee basin, mostly between Reno and Vista where about 3800 acres of agricultural land was flooded (USGS, 1954). Livestock were drowned, crops destroyed, homes were damaged or destroyed, and irrigation facilities were washed out. News reports at the time told of a dike built by the city engineer of Sparks that prevented flooding in three quarters of town (USGS, 1954). Total damages on the Truckee River basin were $3.2 million in 1950 dollars, about $27.3 million in 2007 dollars (Rigby and others, 1998; USGS, 1954). The largest losses were by businesses adjacent to the Truckee in Reno, where department stores, furniture stores, auto sales lots, theaters, the U.S. Post Office, and the two largest hotels in the city were heavily damaged (USGS, 1954). Table 11 lists flood flow data for the November 1950 flood. Downtown Reno flooded during December 1955. Precipitation Frequency Atlas of the United States, a 1000year 7-day rain for this area is about 8 inches! (Bonnin and others, 2003). The degree of flooding was worse in 1955 than in 1950 in most instances (the main exception being the Truckee River at Farad), with this being the record flood at Reno. Nearly 100,000 acres were flooded on the Truckee, Carson, and Walker Basins, more than double the 1950 flood (Rigby and others, 1998) However, damage was not as severe as that experienced from the 1950 flooding, as some flood mitigation and preparation measures had been put in place in the region during the intervening five years (USACE, 1970, 1983). The total estimate of damages on the Truckee, Carson, and Walker river basins was $4 million (1955 dollars; about $30.7 million in 2007 dollars) (Rigby and others, 1998). On the Truckee River basin, there was extensive flooding in Truckee where the Truckee River crested at 7760 cfs (cubic feet per second) on the 23rd, the third largest flood of record at this location. In Reno, the Riverside and Mapes Hotels, located next to the Truckee River on Virginia Street, set up sandbag dikes which were supplemented by pumping. As a result, little damage occurred. However, flooding in downtown Reno was just as extensive as in 1950 (Rigby and others, 1998), where a strip one to two blocks wide on either side of the river from Idlewild Park to the eastern city limits was flooded. However, the flood was well-forecast which allowed advanced preparations and close coordination between agencies which would engage in fighting the flood’s impacts. As a result, flood damage in Reno was limited, with water entering some basements and buildings downtown, and with streets and lawns being buried in debris. However, December 18–25, 1955. Like the November 1950 floods, the December 1955 floods resulted from extremely heavy rainfall combined with unseasonably warm temperatures and melting of the Sierra Nevada snowpack. From December 21 through 24, total precipitation at the headwaters of the principal river basins averaged from 10 to 13 inches (Rigby and others, 1998), with an accompanying 15 inches of snowmelt (USACE, 1970). At Woodfords, California, an unbelievable 14.01 inches of rain fell in the six days between the 18th and 23rd. According to NOAA Atlas 14: Table 12. December 1955 flood flow data. Station Date Peak or Average Daily Flow (cfs) Event Magnitude Truckee River basin Truckee 12/23/1955 7,760 25-year Farad 12/23/1955 14,400 55-year Reno 12/23/1955 20,800 50-year 12/24/1955 6,160 5-year Wadsworth (below Derby Dam) Carson River basin Gardnerville 12/23/1955 17,600 90-year Woodfords 12/23/1955 4,810 65-year Carson City 12/24/1955 30,000 85-year Ft. Churchill 12/26/1955 9,680 25-year 5,180 20-year Walker River basin Coleville 12/23/1955 60 caused "unexpected,” "disastrous,” and "catastrophic" scouring and erosion of the riparian zone on the Truckee River below Reno, especially in the Vista area (Horton, 1997b). The channel of Galena Creek was severely damaged, and two bridges over Steamboat Creek downstream of the mouth of Galena Creek were destroyed. Also, about 1000 feet of U.S. Highway 395 was covered with debris, and many roads in the Truckee Meadows were washed out (USACE, 1972). Without the water storage provided by Lake Tahoe, Donner Lake, Boca, and especially Prosser Reservoirs, the flooding downstream in Reno would have been much worse. The newly constructed Prosser Creek Reservoir began storing water on January 31 and accumulated 16,500 acre-feet during the flood. Rantz and Harris (1963) state: "It is apparent that had Prosser Creek Reservoir not been in operation, the flood peak of February 1 would have exceeded that of 1955 at Reno." Total damage on the Truckee, Carson, and Walker drainages was estimated at $4.4 million in 1963 dollars (about $29.5 million in 2007 dollars) (Rantz and Harris, 1963). Approximately $3.25 million (about $21.8 million in 2007 dollars) of this total was in Nevada, and most of the damages in Nevada were on the Truckee Basin, due to the urbanization in the Reno-Truckee Meadows area (Rigby and others, 1998). Flooding on the Carson and Walker Basins caused major damage to highways, irrigation systems, and ranch land. A total of approximately 32,100 acres were flooded in western Nevada. At the request of Nevada Governor Grant Sawyer, the U.S. Government declared seven western Nevada counties disaster areas as a result of this flooding. These included Churchill, Douglas, Lyon, Mineral, Ormsby (now Carson City), Storey, and Washoe Counties (Rantz and Harris, 1963). Table 13 lists flood flow data for the JanuaryFebruary 1963 flood. damage in Reno totaled only $900,000 (1955 dollars, about $6.9 million in 2007 dollars), less than half the damage which occurred in 1950. About $200,000 (1955 dollars, about $1.5 million in 2007 dollars) in damage occurred in Sparks (USACE, 1970). The Reno airport was flooded to a depth of about 4 feet, stopping all air traffic for several days. About 6000 acres were flooded in the Truckee Meadows east of Reno and Sparks. As with the November 1950 flood, flows below Reno were much less due to the backwater effect caused by the “Vista Reefs” which still existed. However, this is what caused the Truckee Meadows to turn into a vast lake during major floods. Derby Dam, located west of Wadsworth, was overtopped on December 24, causing the dam to fail (Rigby and others, 1998). Table 12 lists flood flow data for the December 1955 flood. January 29–February 2, 1963. As the result of 72 hours of heavy rainfall from January 29 to February 1, 1963, widespread flooding occurred throughout central California and western Nevada. Extensive flooding occurred in Reno, with about 20 square blocks of the downtown area flooded (Rantz and Harris, 1963), similar to the flooding which had occurred in 1950 and 1955. Ten of the 12 bridges in Reno were closed for an extended period (Rantz and Harris, 1963). South Virginia Street was flooded to a depth of 2 feet at Plumb Lane, and hundreds of homes throughout the city were inundated (USACE, 1970). The deepening and straightening work completed by the USACE in August 1962 on the Truckee River below Reno, especially the removal of the Vista Reefs bedrock, helped drain the Truckee Meadows more rapidly than in previous floods (Horton, 1997b; USACE, 1980). However, this work also Table 13. January–February 1963 flood flow data. Station Date Peak or Average Daily Flow (cfs) Event Magnitude February 12–21, 1986. As in all of the large previous floods coming out of the eastern Sierra Nevada, the flooding in February 1986 was caused by heavy rain with high snow levels. However, snow levels during this event were somewhat lower than in the larger events, averaging between 7000 and 8000 feet. Snow levels were as high as 10,000 to 11,000 feet. Flood crests at higher locations (e.g. around Lake Tahoe, Truckee River above Farad, West Fork Carson River, and West Walker River) were higher during a second 1986 flood event which occurred March 7-10. Total damage from this flood was estimated at $17 million, $11 million of which was to public property. The estimate of damage to private property and businesses was $6 million ($11.2 million in 2007 dollars). About 14,000 acres were flooded in western Nevada (Rigby and others, 1998). Although President Reagan declared five northern Nevada counties disaster areas, Washoe County was hardest hit with about $5 million ($9.4 million in 2007 dollars) damage to public property, and about half of that amount was due to damage to roads. Two known fatalities resulted from the flooding. One Sparks man was swept away in flood waters while removing furniture from his home. The other fatality was to an elderly man who suffered a heart attack while shoveling mud and debris from his home (Ekern, 1986). Truckee River basin Truckee 2/1/1963 11,000 45-year Farad 2/1/1963 11,900 35-year Reno 2/1/1963 18,400 40-year Steamboat Cr. 1/31/1963 1,000 10-year 2/1/1963 18,900 40-year 2/1/1963 18,400 25-year Vista Wadsworth (below Derby Dam) Carson River basin Gardnerville 2/1/1963 13,400 45-year Woodfords 2/1/1963 4,890 65-year Carson City 2/1/1963 21,900 45-year Ft. Churchill 2/2/1963 15,300 85-year Walker River basin Coleville 2/1/1963 2,870 5-year Wabuska 2/3/1963 1,470 5-year 61 Table 14. February 1986 flood flow data. Station Date Peak or Average Daily Flow (cfs) Event Magnitude Lake Tahoe and Upper Truckee River basins Upper Truckee R. at S. Lake Tahoe 2/18/1986 1,740 7-year Truckee River basin Farad 2/18/1986 8,237 15-year Reno 2/17/1986 14,400 25-year Steamboat Cr. 2/17/1986 3,600 60-year Vista 2/18/1986 16,100 30-year Wadsworth (below 2/19/1986 16,900 25-year Gardnerville 2/19/1986 7,380 10-year Woodfords 2/19/1986 551 2-year Derby Dam) Carson River basin Carson City 2/18/1986 13,200 20-year Ft. Churchill 2/19/1986 16,600 100-year Coleville 2/19/1986 1,290 2-year Wabuska 2/21/1986 1,370 4-year Walker River basin 62 floods in western Nevada and northern California resulted from several moderate to heavy snowstorms in the northern Sierra Nevada in December 1996, followed by three subtropical, heavy rainstorms from the Pacific, the last of which moved through the region from late December 30, 1996 to early January 2, 1997. Warm tropical-origin storms brought heavy rainfall and associated snowmelt to the region during the first few days of January, which led to near-record to record rain-on-snow flooding on most rivers and streams draining the east slopes of the Sierra Nevada. The Walker, Carson, Truckee, and Lake Tahoe basins received from three to four times their normal precipitation for December 1996 and January 1997. Several locations within these basins exceeded four or even five times their normal precipitation during these two months. An estimated $1 billion in damage (1997 dollars, $1.28 billion in 2007 dollars) occurred in the eastern Sierra and western Nevada from flooding or its consequences, mostly during the first week of the month. Two deaths were reported as a result of the flooding, one in Washoe County and the other in Douglas County. The death in Douglas County occurred in Gardnerville on the evening of the January 2. A 59year-old man was swept into the east fork of the Carson River while operating a front-end loader near its banks. In Washoe County, the death occurred in Sparks on January 3. A 53-year-old man was believed to have Photo by Marilyn Newton. Photo courtesy of Reno Gazette-Journal Flood damages from this flood were highest on the Truckee River basin. However, storage upstream of Truckee Meadows (Tahoe, Prosser, Boca, and Stampede Dams) and channelization through downtown Reno since 1970 prevented a major flood disaster. Also, the fact that snow levels were somewhat lower than in previous large floods helped to a large extent. The most far-reaching impact was due to the Truckee River severing a major natural gas pipeline near Tracy, Nevada. This caused nearly 50,000 Southwest Gas customers in western Nevada and eastern California to have to go without heat for over a week after the flood. Also, avalanches and mud, rock, and debris flows caused closure of Interstate 80 up the Truckee River canyon for almost three days. Heavy snow and avalanches left the Mount Reno-Tahoe International Airport flooded, January 1997. Rose Highway closed for nearly two weeks. Runoff from Peavine Mountain into Lemmon Valley, north fail. The flood washed out the Weeks bridge on U.S. of Reno, threatened several homes and flooded the sewage Highway 95A (Rigby and others, 1998). Table 14 lists treatment plant there (Ekern, 1986). A landslide near Verdi flood flow data for the February 1986 flood. destroyed an old wooden water flume along the Truckee December 29, 1996–January 16, 1997. The flooding of River. Due to the rapidly rising water nearly all of the January 1997 will long be remembered as one of the most bridges over the Truckee River in Reno had to be closed, the significant and devastating flood events in recorded history exceptions were the Wells and Keystone Avenue bridges. on the Walker, Carson, Tahoe, Truckee, and Susan River Serious flood damage was also reported in the Carson basins. An estimated 63,800 acres were flooded in western Valley. The Cradlebaugh Bridge on U.S. 395 over the Nevada (Rigby and others, 1998). The precipitation reCarson River was closed. About 200 residents below El ceived during the two-month period of December 1996Dorado Canyon Dam near Dayton were evacuated as January 1997 was of near-record to record proportions, emergency officials were concerned that the dam might especially in the eastern Sierra Nevada. The New Year's Photo courtesy of Nevada Department of Transportation been swept into the Truckee River. He apparently went to his place of business in order to retrieve some personal belongings. The road to his business was washed away, and it was surmised that he and his truck were swept into the Truckee. According to the Red Cross, an estimated 52 injuries occurred across the eastern Sierra and western Nevada, with four persons requiring hospitalization. Flooding on the Truckee River destroyed or severely damaged many homes, businesses, warehouses, and roads in Placer County, California (including Tahoe City); in Nevada County, California (including the town of Truckee); in Washoe County, Nevada (including Reno, Sparks, Lockwood, Wadsworth, and Nixon), and in Storey County, Nevada (including Lockwood and Mustang). The airport in Reno was closed due to flooding for nearly two days. Interstate 80 running both east and west of Reno was closed for a similar period, as was U.S. Highway 395 which leads north and south. The Truckee Meadows became a lake estimated to cover an area of 3,830 acres. Catastrophic flows on the lower Truckee River were only prevented by the judicious and timely regulation of upstream reservoirs by the Federal Water Master. These reservoirs include Stampede and Boca Dams on the Little Truckee River, Prosser Dam on Prosser Creek, and Martis Dam on Martis Creek. Only Boca Dam was available for such flood prevention purposes in 1950 or 1955. However, if ample storage had not been available in these reservoirs, the 1997 flood event would have been far worse and would have been the record flood. Side of Helms gravel pit in Sparks being washed away beneath westbound lanes of Interstate 80 during the January 1997 floods. On the East Fork, West Fork, and mainstem of the Carson River the January 1997 floods were the worst of record by all accounts: the highest stages, flows, and damages of record. The flooding destroyed or severely damaged many homes and businesses in Alpine County, California (including the towns of Woodfords and Markleeville); Douglas County, Nevada (including Minden, Gardnerville and Genoa); Carson City County, Nevada; and Lyon County, Nevada (including the towns of Dayton and Weeks). The January 1997 flooding was also the worst of record on the East, West, and upper mainstem (above Yerington) Walker Rivers. Extensive flooding on Table 15. December 1996–January 1997 flood flow data. these rivers caused massive destruction in Mono County, California (especially in Walker, Coleville, Peak or Event Topaz, and Bridgeport) and in Lyon County, Nevada Average Daily Station Date Magnitude Flow (cfs) (including Smith, Wellington, Mason, and Yerington). In addition to the flooding, some mountain areas Lake Tahoe and Upper Truckee River basins experienced extensive mud slides and debris flows Upper Truckee R. which closed major arterial highways into the Lake 1/2/1997 5,480 75-year at S. Lake Tahoe Tahoe region. The floods also washed out several Truckee River basin river gages along the three main western rivers (the Walker, Carson, and Truckee), making warnings and Truckee 1/2/1997 11,900 50-year forecasts much more difficult. The river gage on the Farad 1/2/1997 14,900 60-year West Fork Carson River at Woodfords, California was Reno 1/2/1997 18,200 40-year left high and dry when the flood caused the river to reroute itself several yards away. The river gage was Steamboat Cr. 1/1/1997 2,090 25-year soon established at a new location by the USGS. All Vista 1/2/1997 18,500 40-year other damaged river gages were repaired or replaced Wadsworth (below 1/3/1997 19,700 30-year by the USGS. Table 15 lists flood flow data for the Derby Dam) December 1996–January 1997 flood. Carson River basin Gardnerville 1/3/1997 20,300 150-year Woodfords 1/1/1997 8,100 300-year Carson City 1/3/1997 30,500 90-year Ft. Churchill 1/3/1997 22,300 250-year Coleville 1/2/1997 12,300 500-year Wabuska 1/6/1997 2,600 10-year Walker River basin 63 December 30, 2005–January 1, 2006. Rainfall from a series of late December storms caused flooding throughout far western Nevada and the northern and central Sierra. Up to 6 inches of rain fell in the Reno and Carson City areas on December 30th and 31st, with up to 9 inches in the Sierra foothill areas (below about 6000 feet) near these cities. Six to 11 inches of rain fell in the Lake Tahoe basin and along the Sierra crest. The very heavy rain in the Sierra foothills and in the Lake Tahoe Basin was very unusual, and caused Photo by Heather Angeloff significant flooding on many small creeks and streams draining the eastern Sierra. Several had record to near record flooding. Soils were already saturated from storms that occurred earlier in December. Streams and rivers remained high during the last week of the month when another wet storm brought more precipitation from the 26th through the 28th. The storms that occurred from the 26th through the 28th deposited up to 3 inches of precipitation in the Sierra Nevada. Although precipitation totals were less than the previous storm and snow levels were lower, this storm caused large amounts of runoff because soils were still saturated from the storm that ended on the 23rd. This storm caused creeks, streams, and rivers to rise nearly to the levels reached on the 22nd, and again completely saturated all eastern Sierra Nevada and western Nevada watersheds. Rivers and streams receded very slowly and it was apparent on the 28th that any additional rainfall would quickly run off. The most intense storm of the month moved into the Sierra on the 30th. The flooding that occurred was mainly from a “short duration heavy rainfall event with only minor contribution from snow melt” (Wallmann and others, 2006). This was a warm storm with snow levels at almost 10,000 feet. In Washoe County, damage was reported at over 900 businesses in the Sparks industrial area. A levee along Steamboat Creek failed and caused the University of Nevada, Reno agricultural farm in east Reno to flood. Flooding in Lemmon Valley, north of Reno, December 2005. Around 1,800 animals were evacuated to higher ground, but 344 sheep died in the floodwaters. Figure 28 compares the areas that were flooded during the December 2005January 2006 flood with those areas that were flooded during January 1997. Significant flood damage also occurred to homes, businesses, and public infrastructure in Carson City, Storey, Lyon, and Douglas Counties, all of which were declared Federal Disaster Areas. Preliminary total damage to public property in western Nevada was estimated at $16.1 million by the Federal Emergency Table 16. December 2005–January 2006 flood flow data. Management Agency. California counties along the eastern Sierra also suffered significant flood damPeak or ages, with preliminary estimated losses to public Event Average Daily Station Date Magnitude infrastructure at over $15 million. Table 16 lists Flow (cfs) flood flow data for the December 2005–January 2006 Lake Tahoe and Upper Truckee River basins flood. Upper Truckee R. at S. Lake Tahoe 12/31/2005 2,850 15-year Truckee River basin Truckee 12/31/2005 6,030 15-year Farad 12/31/2005 10,100 20-year Reno 12/31/2005 16,400 30-year Steamboat Cr. 12/31/2005 3,600 60-year Vista 12/31/2005 13,700 20-year Wadsworth (below 12/31/2005 Derby Dam) 14,900 20-year Carson River basin Gardnerville 12/31/2005 9,730 20-year Woodfords 12/31/2005 2,720 15-year Carson City 12/31/2005 11,900 15-year Ft. Churchill 1/2/2006 9,800 25-year 12/31/2005 1,805 2-year 1/2/2006 662 2-year Walker River basin Coleville Wabuska 64 FLASH FLOODS During the warmer half of the year (April through September), very little precipitation occurs over western Nevada and the eastern Sierra Nevada. However, the rain that falls during summer thunderstorms can be very intense and can occur during a very short period of time. Due to the intensity of these brief showers the rain that makes it to the surface (the rain that does not evaporate on its descent) does not have time to soak into the hard dry ground. This rainfall runs off and can produce damaging flash floods. A dry river bed can quickly become a raging river if one of these rain showers is overhead. Flash floods can occur at any time of the year but are most common during the period from April through September. During late-summer subtropical moisture is brought into the region from the Pacific Ocean and the Gulf of Mexico. This is the summer monsoon and during its height in July and August large amounts of moismoisture can provide fuel for afternoon thunderstorms. It is these thunderstorms that can cause some of the most intense flash floods. Flash floods can be very destructive. The water in the Figure 28. Map comparing the areas flooded during the December 2005–January 2006 flood with those areas flooded during the January 1997 flood. July 18–27, 1913. Rainfall was reported every one of these days at Reno. Almost an inch of rain (0.91 inch) fell on July 23. The worst damage occurred west of Reno. With so much water flowing out of Galena and Browns Creeks, Pleasant Valley was described as a solid sheet of water. Flood debris covered parts of the Reno-Carson City road (now U.S. Highway 395). A stranded automobile was covered with 25 to 30 feet of debris. Ranch buildings and fences were flooded or destroyed in Pleasant Valley. flash flood can combine with debris such as mud, sand, rocks, and boulders and can cause tremendous damage. Hoyt and Langbein (1955) stated that it “is not unusual for a mudflow to contain about as much solid matter as water.” Roads can be blocked or even washed away. Topography can be extremely important in producing flash floods. Steep slopes can provide the focus for thunderstorm formation, and they can then channel the resulting rainfall swiftly down into the surrounding lowlands (Dietrich, 1979). Flash floods are usually confined to a relatively small area and rarely contribute to mainstem river flooding. Some of the largest and most damaging flash floods which occurred in the region are listed below. June 11, 1927. Torrential rains caused major damage southwest of Reno during the late-afternoon and evening of June 11. Rainfall rates of over 2 inches per hour near the headwaters of Browns Creek caused the Grass Lake Irrigation Reservoir to fail. The resulting flash flood washed out the Mt. Rose Highway just below the dam on Browns Creek. The flash flood killed livestock, flooded the Reno-Carson City highway (now U.S. Highway 395), washed out two bridges, destroyed a house, and flooded ranch buildings and irrigation ditches. The flash flood also washed out over 1000 feet of the Virginia and Truckee Railroad in Pleasant Valley. The heavy rainfall was isolated however. Reno only reported 0.07 inches of rain for the entire day. July 13–18, 1911. Stormy weather occurred in mid July 1911 with thunderstorms being reported each day from July 12 through 19. Heavy rain fell on the 13th with 0.46 inches of precipitation recorded at Reno. Landslides destroyed almost a mile of the Southern Pacific Railroad tracks near Floriston, California. On the new road extending from Reno to Lake Tahoe (the current Mt. Rose Highway) a bridge was washed out over Galena Creek during this flash flood. 65 Photo courtesy of the Nevada Historical Society July 20, 1956. A wall of water reported to be 10 feet high on Galena Creek washed several automobiles off of Mount Rose Highway. Four persons drowned in the flood waters. Farther north this same storm dumped heavy rain on Peavine Mountain, causing the worst flood ever seen on the mountain’s south slopes. The flash flood descended the side of the mountain and destroyed homes and flooded streets in northwest Reno. Businesses were also flooded in the northwest section of downtown. This same area of northwest Reno was flooded by a flash flood the previous July on creeks which were fire-denuded and overgrazed. August 11–19, 1965. Strong thunderstorms over the Sierra Nevada and Lake Tahoe basin caused extensive flash flooding. The heaviest rainfall was on the 15th and 16th around South Lake Tahoe. Mt. Rose Highway was washed out and was closed for three days. Due to the prolonged heavy rainfall Lake Tahoe experienced its latest recorded crest and the gates of the Lake Tahoe Dam at Tahoe City had to be opened to keep the lake level below the legal limit. A mud slide 300 feet wide closed U.S. Highway 395 in Pleasant Valley for three hours. Approximately a mile upstream of Floriston, California, the Southern Pacific Railroad Bridge over Gray Creek was washed out. Large amounts of sediment and debris were introduced into the Truckee River from Gray and Bronco Creeks. Because of this, the cities of Reno and Sparks could not draw water from the Truckee until August 19, and this was only after the Truckee River was diluted by water released from Lake Tahoe and Boca Reservoir. Damage in northwest Reno that resulted from the Peavine Mountain flash flood on July 20, 1956. mud and debris. The landslide-induced flooding caused over $2 million in damages (Glancy and Bell, 2000). It was fortunate that the debris slide did not spill into drainages just a mile to the north (where Davis Creek County Park is located) or to the south (where Bowers Mansion County Park is), since both of these parks were very crowded with visitors, due to the Memorial Day holiday. March 10, 1995. Very heavy rainfall of around one-half inch per hour occurred between 4 pm and 6 pm on March 10, 1995. Moderate rainfall had continued most of the day from around 10 a.m. to 10 p.m. with rainfall totals of between 1 inch and 3.5 inches. The heavy rainfall during the evening, combined with saturated soil and snowmelt, caused a flash flood on Long Valley Creek in Storey County. The Rainbow Bend subdivision was flooded and three bridges over the creek were washed out (including the main access road to the subdivision). With the water main and other utilities impaired, the subdivision was evacuated, and over $2.5 million in damage resulted. May 29–30, 1983. Very rapid melting of a near-record to record snowpack caused many mudslides and flash flooding throughout the eastern Sierra. Two very damaging flash floods are extremely noteworthy. The first occurred around 5:00 am on May 29. On the northwest side of Squaw Valley a 200-foot-wide mile-long mudslide roared down Silver Peak Slope. Over a dozen expensive homes sustained damage, with five of them suffering serious damage. The next day one of the largest flash floods in the area’s history occurred. Around noon on May 30 a huge mudslide started as a 15-acre area at around 8000 feet came loose and slid down the very steep south face of Slide Mountain. This debris spilled into and completely filled Upper Price Lake on Ophir Creek. The water from Upper Price Lake then spilled into Lower Price Lake and then, in a matter of minutes, sent a 15- to 20-foot wall of water, mud, and boulders down Ophir Creek into Washoe Valley and then into Washoe Lake. Traveling at 40 mph the flash flood destroyed everything in its path. One person was killed and four people were injured. Four houses were completely destroyed, and five others were damaged. The flash flood washed out Nevada Highway 429 (old Highway 395) where it crosses Ophir Creek. U.S. Highway 395 was closed because over 600 yards of the highway were covered by Jan. 1–3, 1997. Extremely heavy rainfall, combined with complete melt-off of heavy low-elevation snow cover, caused moderate to severe flash flooding throughout the Lake Tahoe basin, and on streams coming out of the Sierra Nevada and the Virginia Range in the Truckee River basin. Incredibly extensive damage resulted, separate from the huge losses due to the mainstem flooding. June 20–21, 2002. Torrential rainfall produced flash flooding during the evening on both June 20 and 21 in the Spanish Springs area northeast of Reno. Strong thunderstorms produced hail and almost an inch of rain in less than one hour the evening of the 20th. The very next evening strong thunderstorms again formed over the area. An estimated 3 inches of rain fell in about one hour. The runoff, combined with sediment and debris, caused extensive damage. Damage to the area was estimated at over $1 million. Especially hard hit was the new Spanish Springs High School, which suffered over $500,000 damage. 66 FLOOD FREQUENCY IN THE TRUCKEE, CARSON, AND WALKER RIVER BASINS Flood frequency is an estimated measure of how often a particular flood severity may be expected on a river. This information is derived from data from as many past floods as possible (assuming the basin is relatively unchanged during the period) using various statistical methods which are beyond the scope of this report. Flood frequencies for some river gage locations on the Truckee, Carson, and Walker river basins are listed in Table 17. The USGS offices in Carson City, Nevada and Sacramento, California estimated the flood frequencies for all stations using Bulletin 17B, Guidelines for determining flood flow frequency (USGS, 1982). Where flow data are available, the frequency of that magnitude of flow is best expressed as the percent probability that greater than a particular flow will occur in any given year (e.g., "Greater than X cfs has a ten percent chance of occurrence during any year."). However, it is usually expressed as an “X-year flood event”, for example, a “100-year flood event,” by tradition. This does not mean that an X-year flood will happen, on average, every X years. The correct definition of an “X-year flood event” is “the magnitude of a flood which has a 1-in-X chance of being equaled or exceeded in any future oneyear period, given our current knowledge of what has happened in the past.” So, for example, a 100-year flood has a one in 100 (1%) chance of being equaled or exceeded in any one year, a 10-year flood a 1 in 10 (10%) chance, a 2-year flood a one in 2 (50%) chance, etc. Table 17. Peak flow (cubic feet per second) probabilities for the Truckee, Carson, and Walker river basin stations. Frequency (annual probability %) Station USGS # 2-year (50%) 10-year (10%) 25-year (4%) 50-year (2%) 100-year (1%) 10336610 740 2,250 3,510 4,720 6,200 Lake Tahoe and Upper Truckee River basins Upper Truckee River at South Lake Tahoe Truckee River basin Truckee River near Truckee, CA 10338000 1,170 4,590 8,210 12,260 17,870 Truckee River at Farad, CA 10346000 2,750 7,550 11,020 14,100 17,660 Truckee River at Reno, NV 10348000 2,770 9,590 15,300 20,800 27,500 Galena Creek at Galena Creek State Park, NV 10348850 60 460 1,310 2,840 6,100 Steamboat Creek at Steamboat, NV 10349300 140 950 2,010 3,300 5,200 Truckee River at Vista, NV 10350000 3,060 9,900 15,520 20,830 27,240 Wadsworth, NV (below Derby Dam) 10351600 2,344 10,800 18,050 24,900 32,960 Carson River basin East Fork Carson River near Markleeville, CA 10308200 2,520 8,580 14,000 19,400 26,000 East Fork Carson River near Gardnerville, NV 10309000 2,500 6,900 10,500 14,000 18,280 West Fork Carson River at Woodfords, CA 10310000 800 2,200 3,330 4,435 5,790 Carson River near Carson City, NV 10311000 2,440 9,230 15,900 23,030 32,490 Carson River near Ft. Churchill, NV 10312000 2,070 6,440 9,815 12,900 16,540 Carson River below Lahontan Reservoir near Fallon, NV 10312150 1,530 2,430 2,950 3,380 3,840 Carson River at Tarzyn Road below Fallon, NV 10312275 145 930 1,890 3,020 4,610 East Walker River near Bridgeport, CA 10293000 450 1,040 1,450 1,810 2,210 West Walker River below Little Walker River near Coleville, CA 10296000 1,850 4,000 5,480 6,760 8,220 West Walker River at Hoye Bridge near Wellington, NV 10297500 930 2,450 3,860 5,330 7,260 Walker River near Wabuska, NV 10301500 620 2,500 4,045 5,465 7,120 Walker River basin All data are from the USGS. 67 Photo by Tom Roseberry Downtown Reno during the flood of January 1997. View down Truckee River showing Sierra Street, Virginia Street, and Center Street bridges. The Top 25 Weather-Related Events in the Region Since 1850 by Brian F. O’Hara during periods of flooding. Rapid snowmelt can quickly cause rivers and streams to overflow their banks, and these problems can be exacerbated if the snowmelt is caused by or accompanied by heavy prolonged rainfall. Listed below are the 25 weather-related events that have caused the most problems for residents of western Nevada and the eastern Sierra since weather records started to be kept in the mid nineteenth century. It should not be surprising that four of the top 10 events are major floods. Flooding can cause problems on spatial and temporal scales that are not easily matched by other extreme weather events. High winds can cause damage across an area but not all residents may be affected, and the high winds may last only a few hours. A winter storm may bring strong winds and heavy snowfall, but the storm usually moves out of a region after 24 to 36 hours. Roads and sidewalks may be clear of snow by the next day. The very cold air associated with the snowstorm, however, may remain over a region for up to a week after the storm has passed. A major flood is different in that the flood waters can completely inundate an area of tens of square miles. The effects are not isolated as in some thunderstorm or high wind events. All areas below the top of the flood water are Western Nevada and the Lake Tahoe area experience interesting weather each year. Thunderstorms mainly occur during the warmer half of the year, but are more numerous during some summers than during others. Tornadoes and hail are relatively rare, but gusty winds and lightning associated with thunderstorms occur more frequently. Wildfires, whether caused by lightning or humans, can be a tremendous danger from late spring into mid autumn. Dry plants provide fuel for the wildfires, and hot, dry weather conditions can keep wildfires burning for weeks at a time, sometimes threatening homes and entire communities. Significant events also occur during the colder half of the year. Strong winds associated with intense low pressure systems coming in off the Pacific Ocean can cause damage throughout the region. Snowstorms can deposit large amounts of snow and hamper travel for days at a time. The frigid air masses that often accompany these snowstorms can cause dangerously cold temperatures. These cold temperatures, as reflected in extremely low wind-chill indices, can be life-threatening if people are caught outdoors unprepared. Low temperatures can also cause additional problems ranging from frozen pipes to overburdened public utilities. Perhaps the most significant problems occur 68 directly affected. Residential and business areas can become isolated. Those areas in the flood zone are often completely cut off, and the flood waters can remain over an area for days at a time. Roads and sidewalks cannot be cleared of flood waters as they can be cleared of snow cover after a snowstorm. Property in contact with the flood water becomes increasingly damaged. As a result, damage associated with the flood event can cost upwards of $10 million, and oftentimes much more than this. These are some of the reasons why a flood can affect a community much more severely than other weather events might. Among the 25 most significant weather events listed below, winter storms with their heavy snowfall, cold temperatures, and high winds are well represented. However, some of the most significant weather events listed involve major floods. In fact, the most significant event, the January 1997 floods, can certainly be considered one of the major events (weather-related or otherwise) that has affected the region during the last 150 years. debris down Ophir Creek, through Washoe Valley, and into Washoe Lake, all in a matter of minutes. The debris flow washed out Nevada Highway 429 and closed U.S. Highway 395. 21. Waterfall Fire in late July 2004. This human-caused fire burned homes in the foothills west of Carson City. At its height it threatened to spread into Carson City itself, and possibly endangering the capitol and much of downtown. Fortunately, the wildfire was contained before that happened. 20. December 2002 high wind event. Strong synoptic-scale winds caused damage throughout northeast California and western Nevada on December 14. The Reno and Carson City areas suffered extensive damage as the high winds tore roofs off of buildings, blew down fences and signs, and toppled trees. Total damage throughout the area was estimated at almost $10 million. 19. February 16–20, 1990 snowstorm and cold outbreak. Another impressive February snowstorm in the Truckee Meadows but with a colder air mass than the one associated with the February 1959 snowstorm mentioned above. A total of 21.1 inches of snow fell with this storm from February 16–18 at Reno. An incredible 18.0 inches fell just on the 16th. Very cold air filtered into the region with average daily temperatures almost 30° below normal. At Reno the morning low was only 2º above zero on the 18th, and dropped to -7º on the 19th and -6º on the 20th. Due to the very cold temperatures, deep snowcover stayed around for a longer period than in February 1959. Thirteen inches of snow was on the ground at Reno on the 17th. At least 10 inches of snow cover was reported at the Reno airport through the 21st. 25. Snowstorm of early December 1919. A snowstorm during the first five days of December 1919 dumped almost 3 feet of snow on Reno. From December 1 through the 5, a total of 33.6 inches of snow was reported. This was all but 0.2 inches of the month’s total of 33.8 inches. A total of 10.6 inches of snow fell on December 2 and 11.5 inches fell the next day. By the evening of December 5 there was 18 inches of snow on the ground. 24. Record high temperatures in July 2002. This turned out to be the fourth warmest July on record at Reno (behind the Julys of 2003, 2005, 2006). The average temperature for the month was 78.4º. The temperature reached 100º on six days. On both July 10 and 11 the high temperature was 108º, setting an all-time record for Reno. At Carson City the high on the 10th was 105º and on the 11th it reached 104º. The 105º on the 10th is the all-time record high for Carson City. It was around 90º on these dates at Tahoe City. 18. Warm summer of 2003. This was the warmest summer on record at Reno until the summer of 2006. The months of June, July, and September were the warmest June, July, and September on record, and August was the fifth warmest August on record (until the next two years, when August 2004 became tied for the third warmest August on record, dropping August 2003 to sixth place, and then August 2005 became the second warmest August ever, dropping August 2003 to seventh place). With an average temperature of 79.2º July 2003 was the warmest month ever in Reno (a record which stood until the very warm July 2005 when the average temperature for that month was 80.0O). The temperature reached 100º or more on nine days in July at Reno. At Carson City the high temperature on five of those days in July set the record for those dates. 23. February 10–12, 1959 snowstorm and cold outbreak. This was an impressive snowstorm during the second week of February 1959. A total of 21.9 inches of snow fell during the three-day period of February 10–12 at Reno. By the 12th a foot of snow covered the ground at Reno. During the three days from February 11–13, a total of 13.9 inches of snow fell at Carson City. The cold air mass, combined with the deep snow cover, helped daily average temperatures drop to almost 25° below normal. Temperatures dropped into the single digits with morning lows of 5°, 3°, and 8° above zero being reported on February 12th, 13th, and 14th, respectively at Reno. Warmer air returned to the region by the 16th and the snow cover quickly melted. 17. Carson City fire in late September 1926. A wildfire in Clear Creek Canyon south of Carson City destroyed ranches and forest between Carson City and Lake Tahoe. Erratic winds made this fire difficult to control but firefighters kept the fire from entering Carson City. Five men were killed when they were trapped by the fire in a gully in Clear Creek Canyon. 22. Washoe Valley debris flow in May 1983. A 15-acre area on the south side of Slide Mountain slid into Upper Price Lake on Ophir Creek, completely filling the lake. Water spilling out of Upper Price Lake entered Lower Price Lake and sent a 15- to 20-foot wall of water and 69 16. Winter of 1951–1952. This was a severe winter with deep snow and cold temperatures in the Sierra. Heavy snow fell in western Nevada in January and again in March. On March 20 there was 166 inches (13.8 feet) of snow on the ground at Tahoe City (the most in its history). road to choose Lake’s Crossing as their Truckee Meadows site instead of Glendale to the east. As a result, this helped Reno eventually surpass Carson City in population and become the major city in the region. 10. January 14–15, 1988 high wind event. Extremely high winds were reported across western Nevada as a strong cold front moved through the region the night of January 14–15, 1988. A wind gust of 90 mph was reported at the Reno airport. As stated in Storm Data, the “greatest wind speed reported was 106 mph in southwest Reno.” (USDC, 1988). The entry in Storm Data listed the various types of damage that resulted, such as uprooted trees, damaged fences, downed power lines, and broken windows. A roof was torn off of a house in southwest Reno. An estimated $160,000 in damage resulted when a chapel steeple fell through the roof of a high school classroom. Hangars and private planes were damaged at both the Reno and Stead airports. Damage at Stead Airport alone was estimated at between $500,000 and $600,000. Approximately 15,000 residences lost power. 15. March 1907 flood. This flood from March 16 to 23 was caused by heavy rain falling on deep snowcover. Extensive damage occurred throughout the Truckee and Carson River basins. 14. February 3–8, 1989 snowstorm and cold outbreak. Incredibly cold temperatures visited the region during early February 1989. As with the December 1972 storm (mentioned below), snowfall totals were not huge. A total of 9.8 inches of snow fell over the three-day period from February 3 to 5 at Reno. An extremely cold air mass descended over the region with daily temperature averages almost 40° colder than normal. On February 5 the temperature dropped to -10º. The morning low was below zero the next three days with readings of -15º, -16º, and -12º being reported on February 6, 7, and 8, respectively. These low temperatures from the 5th through the 8th remain the record lows for these dates in Reno. The -16º recorded on the 7th is the lowest temperature ever recorded in February in Reno. 9. January 1916 snowstorms. With a total of 65.7 inches of snow, January 1916 is the snowiest month on record at Reno. Four separate snowstorms moved through the region during the month. During the first storm, from January 1 to 5, a total of 10.2 inches of snow fell at Reno. At Tahoe City 31.0 inches of snow fell on January 3 alone. Another 13.8 inches of snow fell at Reno from the 8th through the 10th. The biggest snowstorm of the month (and one of the major snowstorms in Reno’s history) occurred on January 17–18. On the 17th a record 22.5 inches of snow fell, more snow than on any other day in Reno’s history. On the 18th another 3.0 inches of snow fell, giving a storm total of 25.5 inches. The fourth and final snowstorm of the month occurred from the 27th through the 30th with 14.7 inches of snow being reported at Reno. 13. Winter of 1948–1949. Extremely cold temperatures visited the region during the depth of winter. For ten days, from January 23 through February 1, 1949 the morning low dropped to zero or lower each day at Reno. The entire month of January was cold. For 20 days (January 14 through February 2) the morning low dropped to 10º or lower. For 33 consecutive days (January 2 through February 3) the low temperature each morning at Reno was 20º or lower. At Carson City, the -20º reading the morning of January 26 remains its record low for January. 12. Late December 2004 – early January 2005 snowstorms. A pair of snowstorms in late December 2004 and early January 2005 deposited up to 2 feet of snow in the Reno and Carson City areas. Over 3 feet of snow fell in the foothills along the east slopes of the Carson Range. This was the most snowfall that the region had seen since the record-setting snowfall experienced during January 1916. Traffic was paralyzed for days with some side streets not being cleared for two weeks. Fortunately temperatures remained near normal with nighttime lows dropping only into the lower 20s or upper teens during most of the period. Even with close to 20 inches of snow on the ground in mid January, morning lows fell into the single digits on only two days in Reno (the morning low was 6º on the 13th and 8º on the 14th). 8. February 1986 flood. Heavy rainfall contributed to significant flooding over western Nevada and the eastern Sierra in mid February 1986. Two persons died as a result of the flood. The Truckee River basin was the main basin affected. Water storage upstream at Stampede Reservoir, combined with channelization in downtown Reno (completed during the previous 15 years), prevented even greater damage. 7. December 4–11, 1972 snowstorm and cold outbreak. An extremely cold air mass accompanied this snowstorm in early December 1972. Snowfall totals were not overly impressive with 4.8 inches of snow falling on December 4 and an additional 3.1 inches of snowfall being reported at the Reno airport two days later. However, the very cold air mass that settled over the region was almost unprecedented. Temperatures quickly dropped after the snowstorm moved through. The average daily temperature at Reno on December 8 was almost 30° below normal, with a morning low of -12º, and conditions only grew worse. The morning low temperature readings were below zero for the next five days. 11. Late December 1867 – early January 1868 flood. This flooding destroyed all of the bridges in the Eagle and Carson Valleys. In the Truckee Meadows bridges at Lake’s Crossing (now Reno) and Glendale (east of present-day Sparks) were also destroyed. The extensive flooding throughout the region convinced the Central Pacific Rail70 On two of these days the temperature didn’t even climb out of the single digits. The afternoon high on December 9 at Reno was only 6º above zero, and the high on the 11th was 9 above. From the 9th through the 11th the average daily temperatures were more than 30° below normal. The low temperatures on the six days from December 8–13 were 12º, -16º, -11º, -15º, -2º, and -2º, respectively. The low temperatures for the four-day period from the 8th through the 11th remain the record lows for these dates at Reno. The -16º recorded on the 9th is still the official record low for the entire month of December at Reno. this flood than during the flood of 1950. However, flood mitigation and other preparations during the previous five years helped to decrease the potential damage. But the floodwaters covered almost 100,000 acres and affected the Truckee, Carson, and Walker River basins. 2. Late November to early December 1950 flood. This flood was the most severe to affect the region since streamflow records started to be kept in the 1890s. Like many previous floods, this one was caused by heavy rainfall combining with snowmelt from higher elevations. Soils were already saturated from precipitation received earlier in the month, and this contributed to the rapid flooding. Major damage occurred in the Truckee, Carson, and Walker river basins. Reno experienced major damage. All bridges across the Truckee in downtown Reno were closed, with the Rock Street bridge being destroyed. Water was 3 feet deep in much of downtown Reno. Farther south, two new bridges over the Carson River between Carson City and Minden were overtopped, and the Lloyd Bridge southeast of the Nevada State Prison near Carson City was nearly destroyed. 6. Winter of 1889–1890. This was a very cold and snowy winter across the Sierra and western Nevada. The lowest temperature ever recorded at Reno occurred on January 8 when the nighttime temperature bottomed out at -19°F. The temperature fell to -18° on both January 7 and 9. Reports of low temperatures in Carson City ranged from -22° to -27° on January 8 and 9. A total of 31.4 inches of snow fell in Carson City in December, 55.1 inches fell in January, and another 26.9 inches of snow fell in February. 5. Virginia City fire in late October 1875. This fire, driven by strong winds, destroyed Virginia City, at the time the largest city in Nevada. Two persons died and hundreds were left homeless. The mines north of the city were saved, although some mine buildings were lost. The town and mine buildings were reconstructed, but Virginia City had seen its best days. Whether due to the fire or not, Virginia City declined in importance during the next decade. 1. January 1997 flood. This is perhaps the major weatherrelated event in the region’s history. The precipitation that fell during December 1996 and January 1997 was of nearrecord to record amounts, especially in the eastern Sierra. River basins throughout the eastern Sierra and western Nevada were affected, from the Susan River in the north to the Walker River in the south. A major winter storm dropped near-record heavy snow in the Sierra and western Nevada in mid December. A warmer system then brought rain to the region. With snow levels as high as 12,000 feet, rain melted much of the snow cover in the foothills of the Carson Range and Sierra Nevada, and across western Nevada. Mudslides caused much damage in the Lake Tahoe basin. Hundreds of homes and businesses were damaged. The flooding caused the surface of Lake Tahoe to rise to its highest level since 1917. Damage was catastrophic in the Reno and Carson City areas. This was mainly because the area was so built up with businesses and residential areas. The Reno/Tahoe International Airport was forced to close for a day and a half. Many casinos in downtown Reno also had to close. Two deaths and numerous injuries resulted from this major flood. 4. Drought of 1986–94. This was a severe drought, rivaling the prolonged drought of the late 1920s and 1930s. This drought, however, occurred during a period of rapid growth in the Reno, Carson City, and Lake Tahoe region. The lack of precipitation, combined with the population increase, exacerbated growth problems experienced by the region during this period. Washoe Lake was completely dry in the summer of 1989 and again in 1991, the first such occurrences since 1934. 3. Late December 1955 flood. The flooding that occurred during late December 1955 resulted from extremely heavy rainfall. Precipitation at the headwaters in the eastern Sierra averaged over 10 inches, with 15 inches of water being supplied from snowmelt. Flooding was worse during 71 Acknowledgments by Brian F. O’Hara Significant weather events for the region were collected and analyzed using information in the publication Storm Data (USDC, 1959–2005). Significant events were also inferred from the LCDs for Reno. The software program XMClimate proved to be a good comparison to information and conclusions that we derived from manual research. Information about weather events and climatic conditions in rural areas of the region were derived from cooperative weather reports. Cooperative weather observers have been supplying climatological data to the U.S. Weather Bureau and National Weather Service for over 100 years. Their dedicated, selfless service (oftentimes provided by individuals free of charge over periods of decades) has provided an invaluable source of data to the nation to supplement official Weather Bureau and National Weather Service weather and climate observations. Additional information about specific weather events was gathered from newspapers and other publications archived by the Nevada Historical Society in Reno, the Getchell Library at the University of Nevada in Reno, and the Washoe County Public Library in Reno. The staff at the Nevada Historical Society was tireless in their assistance to us. Especially worthy of appreciation are librarian Michael Maher and librarian-assistant Marta Gonzalez-Collins. Their extensive microfilm collection aided in our research of past significant weather events, and their wonderful photograph collection added greatly to our text. We would also like to acknowledge Phillip Earl, curator emeritus of the Nevada Historical Society. He generously shared with us the results of his research into the incredible winter of 1889–90. The staffs at both the Getchell Library and the Washoe County Public Library were of assistance throughout our research in providing access to microfilm and other records when needed. Appreciation is also extended to Gail Prockish, Environmental Engineer II at the Washoe County Department of Water Resources, for creating maps which compared the areas in Reno that were affected by the January 1997 flood and the New Year’s Eve 2005 flood. The authors would also like to thank Randall Osterhuber of the Central Sierra Snow Laboratory (CSSL) for creating the original graph depicting the snowfall and snow depths recorded at that location from the late 1870s to the early 21st century. Many people helped in the review process of this manuscript. The authors would like to thank Roger Lamoni (former Warning Coordination Meteorologist at the NWS office in Reno, and now at NWS Western Region Headquarters), Jim Fischer (Science and Operations Officer), and Jane Hollingsworth (Meteorologist-in-Charge) (both at As with any project, this one could not have been completed without the assistance of a whole host of people. Before the writing could begin, data had to be collected and analyzed. Data for this climatology were derived from a variety of sources. Average values for various parameters were taken from the 1971–2000 climatological normals for Reno, Carson City, and Tahoe City. Actual observed data for these weather parameters are from the monthly Local Climatological Data (LCD) sheets for Reno. Data for Carson City, Nevada and Tahoe City, California were procured from the Western Regional Climate Center (WRCC) website, and from the National Climatic Data Center (NCDC). Weather observations from Carson City and Tahoe City are supplied by NWS cooperative observers. Official data for Reno is from U.S. Weather Bureau and National Weather Service observations. Climate information was also accessed using the XMClimate software program (Petrescu, 1998). Missing data were supplied by the Western Regional Climate Center in Reno and the Nevada State Library and Archives in Carson City. Kelly Redmond, Jim Ashby, and the rest of the staff at WRCC were extremely generous in answering questions. We would also like to thank WRCC for the use of their computer program to generate the wind roses in this publication. Finally, we would like to thank Kelly and Jim for assisting us at the National Weather Service in estimating the snowfall that was experienced at the Reno Airport during the incredible snowstorms of late December 2004 and early January 2005. At that time, the official snowfall and snow depth data for Reno were collected by cooperative weather observers at the Nevada Humane Society, located just east of the Reno airport. These observers were not able to make it in to Reno because of the impassable roads. Without the collaboration mentioned above (using extensive snowfall, precipitation, and snow density data reported from other sites around the region) an accurate estimate of these historic snowstorms would have been unavailable. The staff members at the Nevada State Archives were invaluable in providing access to data that we did not have. Archivist Christopher Driggs and manager Jeffrey Kintop were especially helpful in providing access to actual weather observation forms from the late nineteenth and early twentieth centuries for both Carson City and Reno. This information included weather observation reports from Carson City during the 1890s, and U.S. Weather Bureau weather observation forms for Reno for the period 1906 through 1937. These forms allowed us to supplement data that we were missing from these periods. 72 and climate phenomena abundantly clear. Jennifer Mauldin of the Nevada Bureau of Mines and Geology (NBMG) contributed photographs showing snow cover across western Nevada. Chris Ross, Mark Vollmer, and Jack Hursh also contributed many excellent photographs of various weather phenomena. The Nevada Historical Society made available numerous photographs showing weather conditions from the past across the region. Kris Ann Pizarro, supervising cartographer at NBMG, went out of her way to take photos of weather conditions even as this book was being written. Her dedication to gathering appropriate photographs for this publication is deeply appreciated. Finally, the authors would like to thank Dick Meeuwig, Kris Ann Pizarro, Gary Johnson, and the rest of the staff at the Nevada Bureau of Mines and Geology for their guidance throughout the publication process. Dick was always helpful and was able to make clear what needed to be done in order to complete the publication process successfully. Kris was always generous with her time and was ever willing to answer any questions as they arose. She truly took on this project as her own, and her enthusiasm kept the authors going during those times when progress to them seemed slow. She created many of the figures used in this publication. And Gary’s graphical expertise gave us maps that were truly worth a thousand words. Liz Crouse, Jack Hursh, and Jennifer Mauldin were also involved in seeing this book to publication. All of them were consistently a pleasure to work with, and the authors would gladly go through the experience again. Photo by Jack Hursh the National Weather Service Forecast Office in Reno) for reviewing the draft of this manuscript for accuracy and thoroughness. Their comments were extremely beneficial in improving the final document. Both Jane and Jim gave continual support and encouragement to the authors throughout the research and writing of this book. We would also like to thank Rhett Milne, Warning Coordination Meteorologist (and former Fire Weather program leader) at the NWS office in Reno for his helpful review of the wildfire section. Sincere appreciation is extended to Hal Klieforth (Research Meteorologist Emeritus at the Desert Research Institute (DRI) in Reno, and associate state climatologist for Nevada), Jeffrey Underwood (Nevada State Climatologist, and assistant professor in the Department of Geography at the University of Nevada, Reno), Jim Ashby (climatologist at the Western Regional Climate Center in Reno), and Rachel Dolbier (Administrator of the W.M. Keck Earth Science and Mineral Engineering Museum at the University of Nevada, Reno) for thoroughly reviewing the manuscript as part of the publication process. Their insightful suggestions were invaluable in making this a better document. Photographs have added greatly to this book and the authors would like to thank those persons who offered photos for publication. John James contributed photographs from his collection. His photos of deep snowfall, of drought conditions, and of flooding in the Lake Tahoe basin and in Reno help to make the effects of these weather Snow on Peavine Mountain. 73 References Altine, K., and Dunn, T., eds., 1997, The great flood of ‘97: Reno, NV, Reno Gazette-Journal, 96 p. Garcia, K, 1997, January 1997 flooding in northern Nevada – Was this a “100-year flood”?: U.S. Geological Survey, Fact Sheet FS-077-97, 4 p. Arndt, D.S., and Redmond, K.T., 2004, Toward an automated tool for detecting relationship changes within series of observations: American Meteorological Society, Preprints of 14th Conference On Applied Climate, 9 p. Glancy, P.A., and Bell, J.W., 2000, Landslide-induced flooding at Ophir Creek, Washoe County, western Nevada, May 30, 1983: U.S. Geological Survey and the Nevada Bureau of Mines and Geology, Carson City, Nevada, 119 p. Barbato, G.E., and Hickman, S.F., 1997, Monthly report of river and flood conditions (NWS Form E-5): U.S. Department of Commerce, NOAA, NWS, 13 p. Glickman, T.S., ed., 2000, Glossary of Meteorology (2nd edition): American Meteorological Society, Boston, Massachusetts, 855 p. Bohren, C.F., and Albrecht, B.A., 1998, Atmospheric Thermodynamics: Oxford University Press, New York, 402 p. Goodwin, V., 1977a, Flood chronology, lower half, Carson River subbasin, 1861–1976: Water and related land resources—central Lahontan Basin, Soil Conservation Service, Portland, Oregon, 268 p. Bonnin, G.M., Todd, D., Lin, B., Parzybok, T., Yekta, M., and Riley, D., 2003, Precipitation frequency atlas of the United States, NOAA Atlas 14, Volume 1, Version 3: Silver Spring, Maryland, NOAA, National Weather Service. Goodwin, V., 1977b: Flood chronology, Truckee River subbasin, 1861-1976: Water and related land resources - central Lahontan Basin, Soil Conservation Service, Portland, Oregon, 316 p. Cairns, M.M., Collins, R., Cylke, T., Deutschendorf, M., and Mercer, D., 2001, A lake effect snowfall in western Nevada - part I: synoptic setting and observations: American Meteorological Society, Preprints of 18th Conference on Weather Analysis and Forecasting, p. 329–332. Graedel, T.E., and Crutzen, P.J., 1997, Atmosphere, Climate, and change: Scientific American Library, New York, NY, 196 p. Hess, G.W., and Williams, R.P., 1997, Flood of January 1997 in the Truckee River basin, western Nevada: U.S. Geological Survey, Fact Sheet FS-123-97, 2 p. Davis, K.P., 1959, Forest Fire - Control and Use: McGrawHill Book Co., New York, 584 p. Dietrich, T.L., 1979, Occurrence and distribution of flash floods in the western region: NOAA Technical Memorandum NWS WR-147, National Weather Service, U.S. Department of Commerce, Salt Lake City, Utah, 43 p. Hill, C.D., 1980, The effects of terrain distribution on summer thunderstorm activity at Reno, Nevada: NOAA Technical Memorandum NWS WR-156, National Weather Service, U.S. Department of Commerce, Salt Lake City, Utah, 34 p. Ekern, M, 1986, Report on the February 1986 flood in western Nevada (unpublished manuscript): (Available at the NWS Forecast Office in Reno, Nevada). Hill, C.D., 1993, Forecast problems in the western region of the National Weather Service: an overview: Weather and Forecasting, v. 8, no. 2, p. 158–165. Elliott, R.R., 1987, History of Nevada (2nd edition, revised): University of Nebraska Press, Lincoln, Nebraska, 472 p. Horton, G.A., 1996, Walker River chronology – A chronological history of the Walker River and related water issues: Nevada Division of Water Planning, Department of Conservation and Natural Resources, 91 p. Farnsworth, R.K., and Thompson, E.S., 1982, Mean monthly, seasonal, and annual pan evaporation for the United States: NOAA Technical Report NWS 34, National Weather Service, U.S. Department of Commerce, Washington, D.C., 85 p. Horton, G.A., 1997a, The flood of 1997, final report: An analysis of snowpack water content and precipitation changes in the waterbasins of western Nevada and the effects on runoff and stream flows December 16, 1996 –January 6, 1997: Nevada Division of Water Planning, Department of Conservation and Natural Resources, 211 p. Flora, S.D., 1953, Tornadoes of the United States: University of Oklahoma Press, Norman, Oklahoma, 194 p. Flora, S.D., 1956, Hailstorms of the United States: University of Oklahoma Press, Norman, Oklahoma, 201 p. Horton, G.A., 1997b, Truckee River chronology – A chronological history of Lake Tahoe and the Truckee River and related water issues (seventh update): Nevada Division of Water Planning, Department of Conservation and Natural Resources, 217 p. Fujita, T.T., 1985, The downburst: Microburst and macroburst: SMRP Research Paper No. 210, University of Chicago, Chicago, Illinois, 122 p. 74 Horton, G.A., 1997c, Carson River chronology—A chronological history of the Carson River and related water issues (first update): Nevada Division of Water Planning, Department of Conservation and Natural Resources, 213 p. Osterhuber, R.S., 1993, Climatic summary of Donner Summit, California: USDA Forest Service, Central Sierra Snow Laboratory, Soda Springs, California, 34 p. Osterhuber, R.S., 2001, Climate summary of Donner Summit, California, 1870–2001: University of California, Central Sierra Snow Laboratory, Soda Springs, California, 11 p. Houghton, J.G., Sakamoto, C.M., and Gifford, R.O., 1975, Nevada’s weather and climate: Nevada Bureau of Mines and Geology Special Publication 2, 78 p. Petrescu, E., 1998, Creation and maintenance of a comprehensive climate database: NOAA Technical Memorandum NWS WR-255, National Weather Service, U.S. Department of Commerce, Salt Lake City, Utah, 28 p. Howald, A., 2000, Plant communities, in Smith, G., ed., Sierra east: Edge of the Great Basin: University of California Press, Berkeley, California, p. 94–207. Powell, D., and Klieforth, H., 2000, Weather and climate, in Smith, G., ed., Sierra east: Edge of the Great Basin: University of California Press, Berkeley, California, p. 70–93. Hoyt, W.G., and Langbein, W.B., 1955, Floods: Princeton University Press, Princeton, New Jersey, 469 p. Huggins, A.W., Kingsmill, D.E., and Cairns, M.M., 2001, A lake effect snowfall in western Nevada - part II: radar characteristics and quantitative precipitation estimates: American Meteorological Society, Preprints of 18th Conference on Weather Analysis and Forecasting, p. 333–337. Rantz, S.E., and Harris, E.E., 1963, Floods of JanuaryFebruary 1963 in California and Nevada: U.S. Geological Survey, Water Resources Division, 74 p. Redmond, K.T., 2003, Climate variability in the west: Complex spatial structure associated with topography, and observational issues, in Lewis, W.M., Jr., ed., Water and climate in the western United States: University Press of Colorado, Boulder, Colorado, p. 29–48. James, R.M., 1998, The roar and the silence: A history of Virginia City and the Comstock Lode: University of Nevada Press, Reno, Nevada, 355 p. Kingsmill, D.E., 2000, Diurnally driven summertime winds in the lee of the Sierra: the Washoe zephyr: American Meteorological Society, Preprints of Ninth Conference on Mountain Meteorology, p. 109–112. Rigby, J.G., Crompton, E.J., Berry, K.A., Yildirim, U., Hickman, S.F., and Davis, D.A., 1998, The 1997 New Year’s floods in western Nevada: Nevada Bureau of Mines and Geology Special Publication 23, 111 p. Landin, M.G., and Bosart, L.F., 1989: The diurnal variation of precipitation in California and Nevada: Monthly Weather Review, v. 117, no. 8, p. 1801–1816. Rowe, T.G., Rockwell, G.L., and Hess, G.W., 1998, Flood of January 1997 in the Lake Tahoe basin, California and Nevada: U.S. Geological Survey, Fact Sheet FS005–98, 2 p. Landsberg, H., 1966, Physical Climatology (2nd edition): Gray Printing Co., DuBois, Pennsylvania, 446 p. Sakamoto, C.M., and Gifford, R.O., 1970, Spring and fall low temperature and growing season probabilities in Nevada: University of Nevada Agricultural Experiment Station Bulletin B26, Reno, NV, 50 p. Landsberg, H.E., 1982, Climatic aspects of drought: Bulletin of the American Meteorological Society, v. 63, no. 6, p. 593–596. Sakamoto, C.M., Gifford, R.O., and Koh, Y.O., 1977, Growing degree days in Nevada: University of Nevada Agricultural Experiment Station Report R121, Reno, NV, 64 p. Ludlum, D.M., 1952, The mild and snowy winter of 1951– 52: Weatherwise, v. 5, no. 2, p. 41–44. Ludlum, D.M., 1982, The American Weather Book: Houghton Mifflin Co., Boston, Massachusetts, 296 p. Schroeder, M.J., and Buck, C.C., 1970, Fire Weather: U.S. Department of Agriculture Handbook 360, 229 p. Moosburner, O, and Williams, R.P., 1990, Nevada: Floods and droughts, in Paulson, R.W., Chase, E.B., Roberts, R.S., and Moody, D.W., compilers, National water summary 1988–89: Carson City, NV, USGS WaterSupply Paper 2375, p. 385–392. Scorer, R., 1972, Clouds of the World: Stackpole Books, Harrisburg, Pennsylvania, 176 p. Sellers, W.D., 1965, Physical Climatology: University of Chicago Press, Chicago, Illinois, 272 p. O’Hara, B.F., 2006, Climate of Reno, Nevada: NOAA Technical Memorandum NWS WR-276, National Weather Service, U.S. Department of Commerce, Salt Lake City, Utah, 118 p. Smith, G., 2000, Discovering the eastern Sierra, in Smith, G., ed., Sierra east: Edge of the Great Basin: University of California Press, Berkeley, CA, p. 11–36. 75 Thomas, K.A., and Williams, R.P., 1997, Flood of January 1997 in the Carson River basin, California and Nevada: U.S. Geological Survey, Fact Sheet FS-183-97, 2 p. USDC, 1959-2005, Storm data: U.S. Department of Commerce, v. 1–47. USDC, 1988, Freeze/frost data: U.S. Department of Commerce, Climatography of the U.S. No. 20, Supplement No. 1, 193 p. Trewartha, G.T., 1981, The earth’s problem climates (2nd edition): University of Wisconsin Press, Madison, Wisconsin, 371 p. USDC, 1997, Disastrous floods from the severe winter storms in California, Nevada, Washington, Oregon, and Idaho, December 1996–January 1997: U.S. Department of Commerce, 128 p. Trewartha, G.T., and Horn, L.H., 1980, An Introduction to Climate (5th edition): McGraw-Hill, New York, 416 p. Twain, M., [1872] 1995, Roughing It: University of California Press, Berkeley, California, 853 p. USGS, 1954, Floods of November-December 1950 in western Nevada: U.S. Geological Survey WaterSupply Paper 1137-H, p. 897–955. Uman, M.A., 2001, The lightning discharge: Dover Publications, Mineola, NY, 377 p. USGS, 1958, Surface water supply of the United States 1955, Part 10: The Great Basin: U.S. Geological Survey Water-Supply Paper 1394, 232 p. USACE, 1970, Flood plain information, Truckee River, Reno-Sparks-Truckee Meadows, Nevada: U.S. Department of the Army, Sacramento District, Corps of Engineers, Sacramento, California, 85 p. USGS, 1960, Compilation of records of surface waters of the United States through September 1950, Part 10. The Great Basin: U.S. Geological Survey WaterSupply Paper 1314, 485 p. USACE, 1972, Flood plain information, Steamboat Creek and tributaries, Steamboat & Pleasant Valleys, Nevada: U.S. Department of the Army, Sacramento District, Corps of Engineers, Sacramento, California, 62 p. USGS, 1982, Guidelines for determining flood flow frequency, Bulletin 17B of the Hydrology Subcommittee: U.S. Interagency Advisory Committee on Water Data, USGS Office of Water Data Coordination, 183 p. USGS, 1991, National water summary 1988–89 - hydrologic events and floods and droughts: U.S. Geological Survey Water-Supply Paper 2375, 591 p. USACE, 1974, Reno, Nevada, southwest foothill streams (Evans, Thomas, and Whites Creeks & Skyline Wash): U.S. Department of the Army, Sacramento District, Corps of Engineers, Sacramento, California, 67 p. USACE, 1980, Truckee River, California and Nevada: Hydrology Office Report: U.S. Department of the Army, Sacramento District, Corps of Engineers, Sacramento, California, 92 p. Wallington, C.E., 1966, Meteorology for glider pilots (2nd edition): John Murray, London, England, 302 p. USACE, 1983, Truckee Meadows (Reno-Sparks Metropolitan Area) Nevada, Draft feasibility report and draft environmental impact statement: U.S. Department of the Army, Sacramento District, Corps of Engineers, Sacramento, California, 323 p. Wallmann, J., Barbato, G., Collins, R., Cylke, T., Deutschendorf, M., Fischer, J., Hollingsworth, J., Milne, R., and Shulz, C., 2006, 2005 New Year’s Eve flood assessment (unpublished manuscript): (Available at the NWS Forecast Office in Reno, Nevada). USACE, 1997, Eastern Sierra-western Nevada basins – California and Nevada, Area-wide assessment study: U.S. Department of the Army, Sacramento District, Corps of Engineers, Sacramento, California, 126 p. Washoe County Air Quality Management Division, 2002, Washoe County, Nevada air quality data, 1991–2002, 27 p. Whiteman, C.D., 2000, Mountain meteorology: Oxford University Press, New York, 355 p. USDA Nevada River Basin Survey Staff, 1969, Walker River subbasin, Nevada – California: Soil Conservation Service, Water and related land resources – Central Lahontan Basin, 232 p. Wisler, C.O., and Brater, E.F., 1959, Hydrology (2nd edition): John Wiley & Sons, New York, 408 p. 76 Glossary Diurnal – Referring to the normal variation in atmospheric elements throughout a period of 24 hours. The typical diurnal variation in temperature is for the air mass to cool at night, reaching its lowest point around sunrise. The temperature then rises throughout the day, reaching its highest reading usually in late afternoon or early evening. The relative humidity shows an opposite pattern, reaching its highest reading around sunrise, and then reaching its lowest levels in late afternoon. Acre-foot – The volume of a substance (e.g., water) that would cover an area of 1 acre to a depth of 1 foot. Advection – The horizontal movement of an atmospheric element such as heat, moisture, or fog. Airflow – The movement of air at the surface or at various levels in the atmosphere. Air mass – A body of air that contains nearly uniform constituents such as heat or moisture. Downburst – The downward rush of air produced in a thunderstorm or high-based cumulus cloud. This downward-moving air reaches the ground and then spreads out in all directions. If it hits the ground at an angle, most of the strong wind will move in that direction. Wind speeds can approach 100 mph and cause extensive damage. Damage caused by a downburst can be distinguished from that caused by a tornado because the damage from a downburst tends to lie in the same direction on the ground. By contrast, the damage from a tornado will reflect the rotating motion of the tornado. Antecedent conditions – The conditions of the soil before a weather event. If the soil is saturated, then there is a greater chance that there could be flooding due to runoff from heavy rainfall. Anticyclone – An area of relatively high pressure. The air in this region tends to subside (move downward in the atmosphere). When the air reaches the surface it spreads outward and blows in a clockwise direction around the center of high pressure. Atmospheric pressure – The weight of a column of air from the ground up to the edge of space. The weight of this column is measured by a barometer in a variety of scales: millibars, inches of mercury, among others. Drought – A long period of below normal precipitation sufficiently long enough to cause a serious hydrological imbalance. Cold front – The area of transition between cold air moving into a region and the warmer air it is replacing. Dust devil – A rotating column of air which forms as a result of a hot surface generating strong convection. This relatively warm air then rises and begins to rotate. Wind speeds are considerably less than those in a tornado, but can still cause damage. Condensation – The process which occurs when a substance (such as water) changes from the gaseous to the liquid state. Evaporation – The process which occurs when a substance (such as water) changes from the liquid to the gaseous state. Convection – The vertical movement of heat in an air mass. Convection is responsible for the formation of clouds. Strong convection can lead to the formation of cumulonimbus clouds and thunderstorms. Evapotranspiration – The combination of evaporation and transpiration. Plants release water vapor to the atmosphere. Evapotranspiration refers to the addition of moisture to the atmosphere from things such as bodies of water or snow cover (evaporation) and from plants (transpiration). Cumulonimbus – A type of cloud that forms during unstable conditions. This is the typical “thunderstorm cloud.” It is sometimes referred to by the initials “CB.” The tops of cumulonimbus clouds range from as low as 25,000 ft in the cooler half of the year, to as high as 40,000 ft during the summer in this region of Nevada and California. CBs can produce tornadoes, large hail, strong damaging winds, and lightning. Filling – The process of a low pressure system increasing in pressure and thereby becoming less intense. Fog – Suspended visible water droplets in the atmosphere. Cyclone – An area of relatively low pressure. The air in this region tends to rise. Air outside of this region of low pressure circulates in a counterclockwise direction. Air is pulled into the cyclone to fill the area left by the rising air at the center. Freezing fog – Fog that forms when the temperature is below freezing. Sometimes called pogonip. Freezing level – The altitude in an air mass at which the temperature of the air is 32º F (0º Celsius). It is important for forecasters to know the freezing level in an air mass because this will indicate where snowflakes in the colder air above the freezing level will start to melt and turn into raindrops as they fall through the warmer air below the freezing level. This can also help to indicate at what elevations snowfall will accumulate. Deepening – The process of a low pressure system dropping in pressure and thereby becoming more intense. Depression – Another name for a region of low pressure. Dew point – The temperature at which a parcel of air becomes saturated if it is cooled at a constant pressure. 77 close to the ground. Since warm air is above colder air, an inversion is a relatively stable layer. An air parcel that undergoes lifting will rise into the region of warmer air. Since the air parcel is colder (and thus more dense) than the warmer air surrounding it, it will sink back to the surface. This is why inversions are such notorious fog producers. The cold air sits near the surface and does not mix with warmer air above it. Freezing rain – Type of precipitation that results from raindrops falling through a layer of an air mass that is warmer than 32º F, then falling through a layer near the ground that is colder than freezing. The raindrops do not have time to turn into ice pellets (sleet) but freeze instantly when they hit any surface that is colder than freezing. Front – The area of transition between a cold air mass and an adjacent warm air mass. Jet stream – A region of strong winds in the upper atmosphere. Jet streams are formed from differences in temperature which create pressure gradients. The pressure gradient (difference in pressure across an area) accelerates the air that is moving through this area. There are two main jet streams over the Earth’s northern hemisphere (north of the equator). The polar jet circles the globe at around 50 to 60° north latitude. The generally weaker subtropical jet is located at around 20 to 30° north latitude. Frost – Ice crystals that are formed on surfaces that are colder than freezing. Glaze – A coating of ice caused by freezing rain. Hail – Precipitation that is formed in cumulonimbus clouds. A hailstone starts as an ice particle. As it falls through the cloud it accumulates a covering of water. As it is then forced upward through the cloud the covering of water freezes. A hailstone makes many passes through the cloud until it becomes too heavy for the thunderstorm updraft to keep it aloft. These multiple passes through the cloud are what causes the layering of a hailstone. Very large hailstones are rare in the Great Basin because, among other things, they partially melt as they fall through the very dry air below the cloud base. Lake effect snow – Snowfall that is generated from cold air passing over relatively warmer water. The instability that results allows for convective clouds to develop and increases the possibility of snow to fall. Lenticular cloud – A high-level cloud that is formed by the upward motion in thewave that forms in an air mass in the lee (downwind) of mountains and/or mountain ranges. These clouds have a lens (lenticular) shape because of the air’s motion through the wave. As the air rises and cools in the wave, water vapor is condensed into clouds. Then, as the air in the wave begins moving downward and warms, the cloud droplets evaporate. This undulating motion causes a wave cloud to have a lens (lenticular) shape with its characteristic rounded top and fairly flat base. Headwater – The upper reaches of a river, creek, or stream. High – (see Anticyclone). Humidity – A measure of the amount of moisture in an air mass. Hydrology – The science of water and its interaction with the earth’s surface and subsurface. Lightning – An electrical discharge which results from the difference in electrical charges between the Earth’s surface and a cloud. The rapid expansion of the resulting column of heated air is the sound that we refer to as thunder. Ice pellets (sleet) – Precipitation that results when raindrops fall into a layer of cold air near the surface and freeze before hitting the ground. If the cold air at the surface is not deep enough to cause the raindrops to completely freeze, then they freeze on contact with surfaces when they reach the ground (this is the definition of freezing rain). Low – (see Cyclone). Macroburst – A downburst with winds extending beyond 2.5 miles (4.0 kilometers) from its center. Insolation – (from INcoming SOLar radiATION) The amount of radiation from the Sun that reaches the Earth’s surface (that which is not reflected or absorbed by clouds or the atmosphere). Mainstem - The main part of a river, as opposed to the tributaries which feed into it. Microburst – A downburst with winds extending 2.5 miles (4.0 kilometers) or less from its center. In the Great Basin microbursts tend to by “dry,” meaning that little or no rainfall associated with them reaches the ground. Instability – The vertical state of the atmosphere in which the temperature decreases with altitude, i.e., the lapse rate is greater than the rate of cooling of a parcel of air subject to the process of lifting, thus making the parcel more buoyant than the ambient air and allowing the parcel to rise until it encounters an inversion or a layer with a more stable lapse rate. Millibar – A unit of pressure. The abbreviation for millibar is mb. Inversion – The situation in which relatively cold air underlies warmer air aloft. Inversions are often caused by an extensive snow cover cooling the layer of air Pogonip – A word of Native American origin (meaning “white death”) which is referred to, by some, as freezing fog, which forms in very cold air. The word 78 pogonip has also come to be used by local people living in western Nevada to refer to the rime which coats surfaces as a result of freezing fog. would be in it if the air mass was saturated. If an air mass is saturated it means that evaporation from that air mass equals the condensation occurring in the air mass; its relative humidity is 100%. If an air mass is not saturated (the usual case) then evaporation is exceeding condensation and its relative humidity will be some percentage less than 100%. Polar air – An air mass that has resided over cold polar regions (such as central Canada or central Siberia). The snow covered ground causes the air mass to become extremely cold. This cold air is then transported to lower latitudes as the air mass moves out of its region of origin. Return period – The average period of time between events of a given magnitude. For example, there would be a 1 percent chance that a one-hundred-year flood would occur at a given location in any given year. Polar jet – (see Jet Stream). Precipitation – Water or ice particles that form in clouds and then fall to the surface. Since temperatures in clouds are often below freezing, it is usually snow that forms from the aggregation of ice crystals. If the air below the cloud base is colder than freezing, then the snowflakes will reach the ground without melting. In warmer weather the snowflakes melt into raindrops and reach the surface as rain. If there is a below freezing layer near the surface, depending on the depth of the cold air, raindrops falling through this cold layer will reach the ground as either freezing rain or ice pellets (sleet). Hail is also considered precipitation since it forms in clouds and then falls to the ground. Ridge – A (usually elongated) area of high pressure. Rime – The coating of ice that forms on surfaces when the temperature of an air mass is below freezing. Ripe (snowpack) – The condition of snow that is ready to melt. The density of the snowpack (when the snow is near freezing) is generally greater than 4 parts water to 10 parts snow (so, for example, if 10 inches of ripe snow was melted, it would result in around 4 inches of liquid water equivalent). Runoff – Water (from rainfall or snowmelt) that cannot be absorbed by the ground. This can cause flash flooding or contribute to river flooding. Pressure – See Atmospheric pressure. Saturation – The characteristic of an air mass in which evaporation in the air mass equals condensation. Any additional condensation would result in the formation of clouds, precipitation, or fog. Also, the characteristic of the soil in which the soil cannot absorb any more water. Any water coming into contact with the soil would not be absorbed but would run off. Pressure gradient – The change in pressure between an area of high pressure and an area of lower pressure. Air flows from the area of high pressure to the area of low pressure (this movement of air is what we define as wind). A relatively stronger pressure gradient would thus produce a stronger wind. Radiation – Energy from the Sun which passes through space at the speed of light. As radiation passes through the Earth’s atmosphere some parts of the radiation’s spectrum are reflected by clouds and by ice and snow at the Earth’s surface, and some is absorbed by clouds, water vapor, carbon dioxide, suspended particles, and other matter in the atmosphere. That which is received by the Earth’s surface is absorbed as heat energy which, in turn, warms the lower atmosphere by the processes of conduction and convection. At night, with a clear sky, the ground re-radiates some of its infrared (heat) energy back to space, leaving the lower near-surface air at its minimum temperature near dawn. This diurnal cycle accounts for the large daily temperature ranges experienced during much of the year in our region. Sleet – (see Ice pellets). SNOTEL – (for SNOwfall TELemetry) An observing system that transmits snow water equivalent, snow depth, precipitation, and temperature data in near real -time usually from mountainous sites . Snow level – Similar to freezing level. The snow level is the elevation above which precipitation is generally in the form of snow. Stability – A measure of how easily an air parcel would continue rising if it were forced upward. (for more discussion see Instability). Stable layer – A layer of the atmosphere in which warmer air overlies cooler air. In this situation, if an air parcel is forced to rise through the air mass, it will cool as it rises, thus being cooler than the warmer air it is rising through. Since it is cooler than the surrounding air, its ascent will slow and the air parcel will then fall back to the level it started from. Inversions are examples of stable layers. Rain shadow – The area to the lee of a mountain range which receives a significantly lower amount of precipitation than the windward side of the range. Reach (river) – The length of a river channel, generally between two major tributaries, which is fairly uniform in its discharge and its slope. Stage-discharge relationship – The relationship between the stage at a river gage and the corresponding flow of the river at that point. Relative humidity – The ratio of how much water vapor is in an air mass compared to how much water vapor 79 Stationary front – The area of transition between an area of warm air and an area of cold air. A front is defined as stationary (or quasi-stationary) if it is not moving much, if at all. Warm front – The area of transition between cold air that is moving out of a region and the warmer air that is replacing it. Washoe Zephyr – The westerly (from the west) winds that frequently occur in the lee of the Carson Range, especially during the warmer half of the year. The name is derived from the term for a west wind (zephyr). Storm track – The path that cyclones (low pressure systems) follow. Over the western United States typical storm tracks are through the Pacific Northwest during the summer. During the winter the storm tracks move south and low pressure systems often move through California and the Great Basin. Water equivalent – The amount of water contained in an amount of snow when the snow has been melted. This amount is recorded as the precipitation amount (precipitation is from either rainfall or melted snow). Sublimation – The process which occurs when a substance (such as water) changes directly from the frozen to the gaseous state without passing through the liquid phase. The opposite process is referred to as deposition (however, it is sometimes also referred to as sublimation) in which a substance (such as water) changes directly from the gaseous state to the frozen state without passing through the liquid state. Waterspout – A rotating column of air that is almost always appended to a cloud base and forms over a body of water. Waterspouts form from cumulus clouds, thus they form under different conditions than tornadoes. Waterspouts are much weaker than tornadoes, but still can cause some damage, so boaters are advised to steer clear of them. Subsidence – The situation in which air descends to lower levels. Subsidence occurs in the center of high pressure areas. As the subsiding air reaches the ground surface it moves out in all directions. This subsiding air warms as it moves to lower levels, thus reducing the chance of cloud formation. This is the reason that areas of high pressure usually have clear skies. Water vapor – Water in the gaseous state. Water vapor is always present in the atmosphere but is not visible. Water year – The period (12 months) in which precipitation is recorded for hydrological purposes. A water year runs from October 1 through September 30 of the following year. A water year is designated by the year during which it ends (for example, the water year 1977 would run from October 1, 1976 through September 30, 1977). Subtropical jet – (see Jet Stream). Supercell – An intense long-lasting cumulonimbus cloud. Due to its tilt, a supercell’s updraft and downdraft do not interact, thus allowing the cloud to last for a relatively long period of time, perhaps up to an hour or more. Because of this long life-cycle, large hail and strong damaging downdraft winds can result. However, due to the dry conditions over the region, supercells are rare over the western Great Basin. Wave cloud – The type of cloud that is formed as a result of the motion of the air downwind of an obstacle such as a mountain or mountain range. As the air travels downwind from a mountain range it moves in an undulating manner as a result of its motion being disrupted. As the air moves downward it warms and dries so, as a result, clouds do not form. As the air starts to ascend it cools and a cloud forms. Farther downwind the process continues and as the air descends the edge of the cloud evaporates. This process can continue for tens of miles downwind of the obstacle. Wave clouds are sometimes called lenticular clouds because of their lens shape. Synoptic-scale – In meteorology this refers to large-scale. An example of a synoptic-scale system would be a large area of low pressure or high pressure which covers much of the United States. Synoptic pattern – This is a weather pattern that covers a large area such as much of the United States. Largescale weather systems of this size are referred to as synoptic-scale systems. Wind rose – A diagram depicting the percentage of time (for a day, month, year, etc.) that the wind blows out of various directions (typically eight or sixteen compass points). For each of the compass points, the length of the bar indicates the percentage of time that the wind blows from that direction. Telemetry – The process of transmitting meteorological or hydrological data via electronic means (e.g. telephone line, radio waves, or by satellite). Tornado – A violently-rotating column of air appended to a cumulonimbus (thunderstorm) cloud. Trough – A (usually elongated) area of low pressure with higher pressure on either side of its axis. On pressure charts a trough is usually depicted in the shape of a U or V, or an inverted (upside-down) U or V. 80 Appendix A. Weather Station History Reno When analyzing the climate of a region, changes that have taken place in the observation of weather conditions in the area should be considered. The official weather observation site in Reno has changed a number of times during the last 130 years. Starting in December 1870, daily rainfall observations were taken by the Southern Pacific Company agent at the Southern Pacific Depot at Commercial and Lake Streets in Reno. On January 1, 1888, the official weather observation site was changed to the Administration Building (Morrill Hall) on the University of Nevada campus north of downtown Reno. Beginning in November 1905 the U.S. Weather Bureau took weather observations from the ThomaBigelow Building at First and Virginia Streets in downtown Reno. In March 1910 the observing site was changed to the I.O.O.F (Odd Fellows) Building at Second and North Center Streets in Reno. In March 1934 weather observations were taken at the Post Office Building at South Virginia and Mill Streets. Official weather observations were taken at the Post Office Building until the end of August 1942. With the opening of an airport southeast of town, pilots needed weather observations and forecasts. In January 1931 the U.S. Weather Bureau started taking observations at the airport (Hubbard Field). This was a significant change in that weather observations were now being taken in what could be considered to be almost a rural location. On September 1, 1942, the airport became the official observation site for Reno (and has remained the official site to this day). The effects of this change in location are more pronounced in the temperature record than in the precipitation data (Table A). From the beginning of the century through the 1930s, the average annual temperature at Reno increased 0.5 to 1.0ºF per decade. This may be partially the result of the growth of the downtown area and the simultaneous transition during the early twentieth century from wooden buildings to more brick and stone structures that retain more heat. After the official Weather Bureau observation site was moved to the airport southeast of town the average annual temperature reported during the rest of the 1940s was almost 3.0ºF cooler than it had been during the 1930s and first few years of the 1940s when the observation site was still downtown. The average annual temperature then increased less than 0.5ºF per decade through the 1970s. In fact, there was practically no change in average annual temperature through the 1960s and 1970s. During the 1980s and 1990s the average annual temperature increased at a faster rate (between around 1.0 and 2.0ºF per decade). This is probably due to the “heat island” effect caused by the airport runways and pavement and the increased habitation and use of the area surrounding the airport. No such pattern can be discerned in the precipitation data. The annual precipitation totals are more sensitive to individual events than are the average annual temperatures. The average temperature for the day is only one of 365 such values that will be averaged together for that year. By contrast, a few very large snowstorms during a particular decade can skew the data. In just one day one large winter snowstorm or spring rain shower can deposit a tenth of Reno’s annual precipitation. An example of the significance of this precipitation data can be seen during the drought years from the mid 1920s through the early 1930s. During the first few years of the decade an inch or more of precipitation was reported at Reno on one or two days each year. However, after 1.02 inches of precipitation (0.20 inches of this from melted snow) was reported on December 13, 1922, it was seven years before at least an inch of daily precipitation was again recorded at Reno when 1.13 inches of rain fell on December 10, 1929. After the move to the airport in September 1942, the next change in observation site at Reno occurred in June 1949 when the weather observation equipment was moved 60 feet to the south to the CAA Building at the airport. Another change took place in October 1959 when the equipment was moved 0.8 mile to the north-northwest to the Federal Facilities Building at the airport. In August 1980 the observing equipment was moved a quarter-mile to the east-southeast to the General Aviation Building on the airport grounds. Table A. Average annual temperature (ºF) and precipitation (inches) per decade during the twentieth century at Reno. Decade Temperature Precipitation 1900–1909 49.8 8.60 1910–1919 50.2 8.15 1920–1929 51.0 6.92 1930–1939 51.9 6.99 1940–1942 51.7 8.19 Official weather observations relocated from downtown Reno to Reno airport (Hubbard Field) starting September 1, 1942. 81 1943–1949 49.0 6.04 1950–1959 49.2 7.76 1960–1969 49.5 7.70 1970–1979 49.5 7.05 1980–1989 51.2 7.86 1990–1999 52.3 7.65 On May 1, 1923, the Sierra Pacific Power Company office on Main Street in Carson City became a cooperative observer for the U.S. Weather Bureau. In June 1941 the observation site was transferred to the roof of the Laboratory Building of the Nevada Department of Highways at the northwest corner of West Second and Carson Streets. In July 1951 the observation location was moved two blocks east to the State Office Building on Fall Street between Second and Third Streets. In May 1965 the observing site was moved 0.4 miles south to the new Highway Testing Laboratory and Headquarters Building of the Nevada Department of Highways. In May 1984 Station House #3 of the Carson City Fire Department (on North Curry Street) became the official cooperative weather observer for Carson City. This was 2 miles south of the previous location. In June 1992 the location of Station House #3 was changed to 777 South Stewart Street. Weather observations were taken at the Reno airport (through all of its subsequent name changes) by Weather Bureau (and later National Weather Service (NWS)) personnel from 1931 until 1995. A significant change occurred on September 1, 1995 when an automated weather observing system was commissioned at the Reno airport. On May 5, 1998, this automated observing system was moved from the south end of the airport runway to its current location at the north end. This automated system is a new way to take weather observations and this should be taken into account (as would changes in location) if any change in weather patterns or climate is noticed in the future (Arndt and Redmond, 2004). A significant drawback with this automated system is that snowfall and snow depth observations are not taken. This effectively ended snowfall and snow depth data for the Reno airport location until the fall of 2004 when a cooperative weather observer near the airport started recording snowfall and snow depth data. Tahoe City Cooperative weather observations have been taken at Tahoe City since 1914. The observation site has been in virtually the same location until present. The Tahoe station started out at latitude 39º10'N and longitude 120º10'W in the Truckee River valley at an elevation of 6500 feet, approximately 500 feet from Lake Tahoe. In August 1950 the equipment was moved approximately 125 yards east of its former location to the other side (south bank) of the Truckee River about one-half mile southwest of the U.S. Post Office in Tahoe City, and 300 feet south of the mouth of the river. The station was at the same latitude but the new longitude was 120º08'W and the new elevation 6230 feet. In July 1960 the name of the station was changed from Tahoe to Tahoe City, to agree with that of the post office. In September 1971 the equipment at the Tahoe City location was moved 475 feet to the north-northeast, to a location 425 feet south of the Lake Tahoe outlet. Carson City According to the Nevada State Library and Archives, Charles W. Friend started taking weather observations in Carson City in 1880. His weather observatory was a block from the state capitol. In 1887 the Nevada state legislature established a Nevada State Weather Service, and Friend was appointed as its first director. After the establishment of the U.S. Weather Bureau in 1890 weather observers from the Bureau were assigned to assist Friend in Carson City. Starting in 1892 a representative from the Weather Bureau held the position of assistant director of the Nevada State Weather Service. The state weather service continued until 1905 when responsibility for official weather observations was transferred from personnel in Carson City to the Weather Bureau office in Reno. 82 The Nevada Bureau of Mines and Geology (NBMG) is a research and public service unit of the University of Nevada and is the state geological survey. NBMG is part of the Mackay School of Mines at the University of Nevada, Reno. NBMG scientists conduct research and publish reports on mineral resources, engineering geology, environmental geology, hydrogeology, and geologic mapping. Individuals interested in Nevada geology are encouraged to visit, call, or write NBMG or visit our homepage at www.nbmg.unr.edu. NBMG publications and maps, U.S. Geological Survey maps, and related publications can be purchased at the Publication Sales Office or ordered over the Internet at www.nbmg.unr.edu/sales.htm. Orders for publications or requests for information may also be made by telephone, fax, e-mail, or U.S. Mail. Phone: (775) 784-6691 Phone hours: 7:00 a.m. to 4:00 p.m., Monday –Friday Fax: (775) 784-1709 E-mail: (orders) [email protected] (information) [email protected] U.S. Mail: Nevada Bureau of Mines and Geology Mail Stop 178 University of Nevada Reno, NV 89557-0178 Fog and frost rime in a pine forest in the Carson Range, March 2005. Photos by Heather Angeloff The University of Nevada, Reno is an Equal Opportunity/Affirmative Action employer and does not discriminate on the basis of race, color, religion, sex, age, creed, national origin, veteran status, physical or mental disability, and in accordance with university policy, sexual orientation, in any program or activity it operates. The University of Nevada, Reno employs only United States citizens and aliens lawfully authorized to work in the United States. Manuscript reviewed by: Jim Ashby, Western Regional Climate Center, Reno Rachel Dolbier, W.M. Keck Museum, UNR Hal Klieforth, Desert Research Institute, Reno Jeff Underwood, Department of Geography, UNR Editing and layout: Dick Meeuwig Graphics and photo enhancement: Kris Ann Pizarro and Jennifer Mauldin Production: Jack Hursh First edition, first printing, 2007, 1000 copies Printed by: Bear Industries, Sparks, Nevada Photo by Jack Hursh Photo by Mark Vollmer Downtown Reno, 2002. Snow is falling on Slide Mountain (elevation 9694 feet) in the background. Note the avalanche paths down the middle part of the mountain with ski runs on both sides. Southern Reno, looking northeast toward a rainstorm beyond the Huffaker Hills.