Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
NWS State College Case Examples The Big Chill of January 2013 By Richard H. Grumm And Elyse Colbert National Weather Service State College, PA 1. Overview The period of 15-27 January saw the incursion of arctic air into eastern North America and much of the north-central and northeastern United States. During the peak of the cold episode (Fig. 1) a deep trough with -2 to -3s height anomalies (Fig. 1a) and a pool of deep cold air (Figs. 1b&1c) were present over much of eastern Canada and the northern tier of the United States. Much of the North America was dry with large areas where the precipitable water (Fig. 1d) was near or below normal. The strong and persistent ridge over the southwestern Atlantic limited the penetration of the cold air into the southern and southeastern United States. A sudden stratospheric warming (SSWE:Smith and Kushner 2012; Baldwin et al. 2012) event was observed in long range forecasts in late December 2012 and early January 2013. SSWE events are typically monitored above 50 km and temperatures on model pressure surfaces of 70 to 10 hPa are often examined to monitor these events. Baldwin and Dunkerton (2001 hereafter BD2001) noted that stratospheric events often follow the arctic oscillation (AO). Observational studies suggest that SSWE events be used to predict changes in weather regimes. Large warm ups over the Polar Regions often lead to arctic outbreaks over North America. BD2001 entitled their paper “Stratospheric Harbingers of Anomalous weather Regimes” due to the apparent observational predictability component of such events. During most winters, in the January to February time frame there is typically 1 major stratospheric warming event (Kuttippuarth and Nikulin 2012). It will be shown that during early January 2013 there was a northern hemispheric SSWE. During the onset of the SSWE event, conditions had been relatively warm over most the eastern United States. Through December through about 6 January a cold pocket was present over the pole at 10 hPa which was replaced by a ridge and above normal temperatures after 6 January 2013 (not shown). The strong ridge over the southwestern Atlantic (Fig. 1a) was dominant feature through first half of January 2013, producing generally warm weather over most the eastern United States. High temperature records were tied or broken during a prolonged period in the southeastern United States (Table 1) through 18 January 2013. A surge of warm air ahead of the first blast of cold air tied or broke over 100 daily maximum temperatures records from 12-13 January 2013 in the eastern United States. The warmth then emerged over the southwestern United States (Table 1). A second surge of record warmth would affect most of the eastern United States as the cold air slowly retreated on 27-28 January. NWS State College Case Examples This paper examines the pattern of January 2013 with a focus on the evolution of the big chill of mid-January 2013. The persistent ridge over the southwestern Atlantic precluded the intrusion of the cold air into the citrus growing regions of the southern United States. Forecasts of the event are presented showing that the event and pattern change were relatively well predicted. Finally, this event and its associated pattern are compared to the arctic outbreaks of January 1985 and 1994. 2. Data and Methods The large scale pattern was reconstructed using the Climate Forecasts System (CFS) as the first guess at the verifying pattern. The standardized anomalies were computed in Hart and Grumm (2001). All data were displayed using GrADS (Doty and Kinter 1995). The daily record temperature data were obtained from the National Climate Data Center (NCDC) website using the interface on this site. Data retrieved included the date, number of records set or tied and the spatial context was estimated from these data. The record high, lows and record low highs and record low highs were all tabulated and examined. The precipitation was estimated using the Stage-IV precipitation data in 6-hour increments to produce estimates of precipitation during the month of January 2013. Daily records are based on the NCDC data set similar to that used to compute the daily number of record highs and lows used in Tables 1 & 2. The NCEP global ensemble forecast system (GEFS) data were used to show the larger scale forecasts of the pattern and the peak intrusion of the cold air into the eastern United States. Overall, large scale models did not indicated a high probability of a transition to a colder pattern in the eastern United States. 3. Observations The high and low temperature records tied or set during January 2013 (Tables 1 & 2) and plots of these data (Fig. 2) show the impact of the change in the pattern over the United States during the middle of January 2013. There was a distinct shift from cold to warm in the western United States and a gradual erosion of the warm conditions in the southeastern United States. Despite the change in the pattern, the cold air mass that affected the eastern United States did not set many low temperature records. These data show a decrease (Table 1 and Figure 2b) in the number of record high temperatures tied or exceeded after 13 January as the cold air pushed most of the warm air out of North America and the United States. The warm air did not return until the cold air retreated on 27-28 January. The extreme warmth of 27-29 January is a topic for potential farther research. NWS State College Case Examples As the cold air and pattern change took hold, there was an increase in the number of record low temperatures tied or exceed. However, the axis of Figure 2 shows that the warm events outnumbered cold events by nearly 2:1 when comparing the warmest to coldest days. The record low maximum temperatures to show the influx of the cold air but they too are generally limited to fewer than 200 records tied or broken per day during the peak of the cold episode. The 2:1 ratio can also be obtained comparing the total number of records tied or broken which shows that January 2013 had nearly twice as many warm records set or tied relative to cold records set or tied. 4. Pattern-Tropospheric The pattern over North America from 01-15 January 2013 (Fig. 3) showed the persistence and the strength of the ridge over the southwest Atlantic where for 500 hPa height anomalies were +1s above normal during the period. A strong ridge was present over the eastern Pacific basin. A weak 500 hPa low was located over extreme northern North America. The ridge over the western Atlantic extended over most of the eastern United States and Great lakes. Beneath the ridge the 700 and 850 hPa temperatures were above normal. The only cold air of note was over the West Coast of North America. The pattern from 15-23 January 2013 (Fig. 4) is a stark contrast to the data in Figure 3. The eastern Pacific ridge was replaced by a sharp ridge along the West Coast of North America and a strong vortex was present at 500 hPa over central Canada. Cold dry air was present over most of central and northern North America. The strong ridge over the southwestern Atlantic was still present though suppressed to the south and east. This ridge limited the southward extent of the surge of cold air into the Gulf States and Florida. The evolution of the cold in the United States is shown in Figures 5 & 6. These data show the surge of above normal 850 hPa temperatures over most of the United States East of the Rocky Mountains from 12-14 January 2013. This encompassed the period of above normal warmth in Table 1 and Figure 2. The arctic air, with 850 hPa temperatures around -34C in its core began to enter the northern United States at 17/0000 UTC (Fig. 5f). Figure 6 shows the intrusion of cold air across the northern tier of the United States with a -30C contour at 850 hPa over Great Lakes at 22/0000 UTC. The core of the cold air over the Great Lakes and eastern United States at 22/1200 UTC is shown in Figure 7. The -20C contour was well into the Ohio Valley with -28C air at 850 hPa over the Great Lakes (Fig. 7b). The cold air was also in a tight gradient between the cyclone off the East Coast and the anticyclone over the western plains (Fig. 7d). The lack of a significant number of low temperature records being broken or tied may relate to how cold the air mass was relative to other mid-January air masses. Table 3 lists cold days from the COOP station in State College, PA. The dates show many record lows or record high lows associated with cold days over the region. The pattern associated with the cold episodes of NWS State College Case Examples January 1994 and January 1985 is shown in Figure 8 & 9. The 1985 event had a pocket of -32C air at 850 hPa over the Ohio and it was the second coldest 24 hour period in State College. The January 1994 event had a stronger surface anticyclone over the eastern United States, the coldest temperatures at 850 hPa were observed at 19/1200 UTC, prior to the arrival of the massive anticyclone, along with deep snow cover produced the extreme low temperatures on 21 January 1994 (Table 3). 5. Stratosphere Figure 10 shows the 50 hPa temperature for 15 December 2012, 20 January 2013, the change of the 50 hPa temperatures from 31 January through 31 December and for the period covered by the first two periods. These data showed a cold pocket over the pole and northern Europe on 15 January which was replaced by a warm pocket by 20 January 2013. A change of over +30K is clearly visible over and near the poles. The largest changes occurred from 31 December through 20 January (Fig 10c) thought there was large change in the longer period of 15 December 2012 through 20 January 2013. These data show that there was an impressive SSWE from late December 2012 through midJanuary 2013 and this SSWE event was related to an arctic outbreak over much of eastern North America. Though not shown, this warm-up was predicted in the GFS and ECMWF in late December (not shown). 6. Forecasts The 500 hPa pattern valid at 1200 UTC 17 January from the NCEP bias corrected GEFS is shown in Figure 11. Forecasts for 0600 UTC 10 January and 15 January are presented. These forecasts were somewhat randomly selected though any forecast from the period of 5 to 15 January would illustrate the point as these data cover 16 days and the general cold trend was present 16 days in advance. These forecasts show the deep trough over eastern North America with below normal heights and the below normal 850 hPa temperatures, which correspond well with the surge of low temperature records in Table 2 and Figure 2. These to comparative forecasts show that the ensemble mean under predicted the depth of the trough and the intensity of the cold air 7 days out, likely due to the large spread between the members, relative to the shorter 2-day forecasts. This impacted the standardized anomalies. But the big differences included the -32C contour and 4800 m contour in the sharper, shorter range forecasts. The salient point here is the cold episode was generally well predicted. 7. Summary NWS State College Case Examples A deep trough brought a surge of cold air into eastern North America in mid-January 2013. The surge of cold air and the deep trough were relatively well predicted by the NCEP GEFS, though only GEFS bias corrected data are shown here. The SSWE event of late December and early January 2013 also appeared to be a useful tool to add confidence in anticipating the surge of cold air into eastern North America. Despite the cold air, the daily number of record lows set during the period was rather paltry this may be related to the large ridge over the southwestern Atlantic and other factors. As the long wave pattern shifted over North America in January, cold air moved into the United States and the number of tied or broken low temperature records began to rise (Table 2) around 12 January, though most of the records were broken in the western United States. The larger impact was to reduce the number of high temperature records set during January. There was a peak in high temperature records being tied or set as the cold air moved southward and the warm air associated with persistent western Atlantic subtropical ridge pushed warm air northward ahead of the frontal system. The surge of cold air into the central and eastern United States from 15 to 24 January 2013 did not set a significant number of low record temperatures. The data in Tables 1 & 2 and Figure 2 imply that despite the cold, the number of high temperatures broken during the month of January 2013 was far larger than the number of record lows and record low high temperatures. This could be the result of the a) the lack of deep snow cover over a large portion of the region affected by the cold air, b) the general lack of extreme cold air over North America due to climate change or c) the cold episode occurred during a time where historically there have been intrusions of extreme arctic air masses. The arrival of the arctic air in this event was well timed to coincide closely with a record cold episode in January 1994. The colder air mass of 1994 relative to 2013 may imply that point b) may have some merit. This is further supported by the fact that the month of January, despite the intrusion of cold air, had more record warm events than cold events. An argument often presented by climate change research showing the tendency for more warm episodes and records relative to cold episodes and records being set. The large scale pattern during the first 3 weeks of January 2012 showed a ridge off the southwestern Atlantic (Fig. 1) which support return flow on its flanks. This return flow produced over 150 mm of rainfall from eastern Texas to southern Virginia (Fig. 12). There was over 300 mm of precipitation along the Gulf Coast during the first 24 days of January. The flow about this ridge and the cold air to the north limited the precipitation in the southern and central plains and kept most of the northern tier of the United States relatively dry. The Pacific Northwest too experienced relatively wet conditions. NWS State College Case Examples The large scale ridge over the southwestern Atlantic may have limited how deep into the southeastern United States the cold air penetrated. This too may have limited the number of record low temperatures set or tied in January 2013. This event appears to show that SSWEs may be useful “harbingers” of arctic outbreaks into eastern North America. This event may also suggest that the cold air mass of 2013 may have lacked the deep cold of similar air masses of 15 to 50 years ago. Or quite simply put, arctic air over North America appears to lack the punch of arctic air from 20+ years ago. 8. Acknowledgements Data access to daily highs, lows, and precipitation courtesy of NCDC. 9. References Baldwin, M.P. and T.J. Dunkerton, 2001: Stratospheric harbingers of anomalous weather regimes, Science, 244, 581-584. Baldwin, M.P., and T.J. Dunkerton, 1999: Downward propagation of the Arctic Oscillation from the stratosphere to the troposphere, J. Geophys. Res., 104, 30,937-30,946. Doty, B.E. and J.L. Kinter III, 1995: Geophysical Data Analysis and Visualization using GrADS. Visualization Techniques in Space and Atmospheric Sciences, eds. E.P. Szuszczewicz and J.H. Bredekamp, NASA, Washington, D.C., 209-219. J. Kuttippurath and G. Nikulin, 2012: A comparative study of the major sudden stratospheric warming’s in the Arctic winters 2003/2004–2009/2010. Atm. Chem. Phys,12,8115-8129. Miller, J.E. 1946: Cyclogenesis in the Atlantic coastal region of the United States. J. Meteor.,3,31-44. Smith, K. L., and P. J. Kushner (2012), Linear interference and the initiation of extratropical stratospheretroposphere interactions, J. Geophys. Res. NWS State College Case Examples Figure 1. Composite pattern from the CFSV2 data for the period of 0000 UTC 15-23 January 2013 showing a) 500 hPa heights and height anomalies , b) 700 hPa temperatures and temperature anomalies, c) 850 hPa temperatures and temperature anomalies, and d) precipitable water and precipitable water anomalies. Return to text. NWS State College Case Examples NWS State College Case Examples Figure 2. Number of record highs, record lows, and record low high temperatures set or tied during January 2013. Return to text. NWS State College Case Examples MAX TEMPS Date 1/1/2013 1/2/2013 1/3/2013 1/4/2013 1/5/2013 1/6/2013 1/7/2013 1/8/2013 1/9/2013 1/10/2013 1/11/2013 1/12/2013 1/13/2013 1/14/2013 1/15/2013 1/16/2013 1/17/2013 1/18/2013 1/19/2013 1/20/2013 1/21/2013 1/22/2013 1/23/2013 1/24/2013 1/25/2013 1/26/2013 1/27/2013 1/28/2013 1/29/2013 1/30/2013 1/31/2013 Total: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 New Records 1 1 1 1 2 0 1 2 14 15 48 200 159 77 49 25 27 11 37 25 11 23 27 28 27 13 19 56 270 345 147 1662 Ties 1 3 5 0 2 1 1 8 16 9 19 69 78 46 16 17 12 5 14 15 10 10 11 12 15 9 13 21 71 91 28 628 Sum 2 4 6 1 4 1 2 10 30 24 67 269 237 123 65 42 39 16 51 40 21 33 38 40 42 22 32 77 341 436 175 2290 Locations Alaska SE, West Coast NW Coast Florida NW Coast NW Coast West Coast Florida, Michigan Florida (majority), Upper Mississippi Valley Florida, Upper Mississippi Valley Mississippi Valley, Florida Southeast, Midwest Alaska, Southeast, Midwest Alaska, Southeast Southeast Southeast Southeast Southeast Midwest Midwest Southwest Southwest Southwest Colorado, Texas Colorado, Texas Texas, Montana Texas, West Texas, Southern Plains Midwest Midwest to Ohio Valley Mid Atlantic, Northeast Table 1. List of Daily high temperatures set and the region or regions of the United States affected. Data from NCDC including the date, day of month, new records, tied records, total records and region or regions with most records set or tied. Return to text. NWS State College Case Examples Date 1/1/2013 1/2/2013 1/3/2013 1/4/2013 1/5/2013 1/6/2013 1/7/2013 1/8/2013 1/9/2013 1/10/2013 1/11/2013 1/12/2013 1/13/2013 1/14/2013 1/15/2013 1/16/2013 1/17/2013 1/18/2013 1/19/2013 1/20/2013 1/21/2013 1/22/2013 1/23/2013 1/24/2013 1/25/2013 1/26/2013 1/27/2013 1/28/2013 1/29/2013 1/30/2013 1/31/2013 Total: Day of Month 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 New Records 6 11 23 9 19 15 5 2 1 2 8 44 69 115 90 45 11 6 4 9 10 22 7 4 2 4 0 2 3 0 1 549 Ties 4 4 11 2 3 2 0 0 0 0 3 15 16 26 14 15 7 2 5 2 7 6 4 1 1 3 0 0 2 0 0 155 Sum 10 15 34 11 22 17 5 2 1 2 11 59 85 141 104 60 18 8 9 11 17 28 11 5 3 7 0 2 5 0 1 704 Locations West West West West West/Southwest Southwest West West West Gulf Coast Southwest West West West West West West Southwest West West West West, Midwest West West, Minnesota Mid Atlantic Southwest Southwest Arizona Table 2. As in Table 1 except for the number of low temperature records set. Return to text. NWS State College Case Examples Figure 3. As in Figure 1 except for 0000 UTC 1-15 January 2013. Return to text. NWS State College Case Examples Figure 4. As in Figure 1 except for the time period of 0000 UTC 15-23 January 2013. Return to text. NWS State College Case Examples Figure 1. As in Figure 1 except for 850 hPa temperatures and temperature anomalies at 0000 UTC from a) 12 to b) 17 January 2013. Return to text. NWS State College Case Examples Figure 6. As in Figure 5 except for 850 hPa temperatures and temperature anomalies at 0000 UTC from a) 17 to b) 22 January 2013. Return to text. NWS State College Case Examples Figure 2. CFSV2 data showing the pattern at 1200 UTC 22 January 2013 including a) 500 hPa heights and height anomalies, b) 850 hPa temperatures and temperature anomalies, c) precipitable water and precipitable water anomalies, and d) mean sea-level pressure and pressure anomalies. Return to text. NWS State College Case Examples Date Min Max 2 Feb 1899 -20 -5 1/21/1985 -17 -3 1/18/1982 -17 -2 1/20/1994 -18 -1 1/18/1977 -11 -11 1/23/1936 -14 7 1/30/1977 -10 9 1/17/2009 -2 8 1/16/1994 -6 3 1/1/1963 -3 10 1/13/1977 -1 11 1/19/1976 -1 15 1/11/1978 -2 12 2/12/2008 2 16 1/22/1966 4 11 1/24/2003 4 12 1/21/2008 7 14 Table 3. List of dates and 24 hour maximum and minimum temperatures at State College, PA. Return to text. NWS State College Case Examples Figure 8. As in Figure 7 except for 0000 UTC 20 January 1994. Return to text. NWS State College Case Examples Figure 9. As in Figure 7 except for 0000 UTC 21 January 1985. Return to text. NWS State College Case Examples Figure 10. CFSRV2 50 hPa data showing stratospheric temperatures ( C) over the northern hemisphere at a) 0000 UTC 15 December 2012, b) 20 January 2013, and the 50 hPa temperature changes from c)20 January 2013 and 31 December 2012 and d) 20 January 2013 and 15 December 2012. Time differences are at 0000 UTC for the specified times only. Return to text. NWS State College Case Examples Figure 12. Stage-IV summed precipitation from 0000 UTC 1 January through 0000 UTC 24 January 2013. Values in mm and values less than 8 mm not shown. Return to text. NWS State College Case Examples Figure 11. GEFS bias corrected forecasts of 500 hPa heights and 850 hPa temperatures and standardized anomalies showing the forecasts valid at 1200 UTC 17 January 2013 from forecasts initialized at a) 06 UTC 10 January 2013 and right) 0600 UTC 15 January 2013. Upper panels are the 500 hPa forecasts and lower panels the 850 hPa temperatures forecasts from each day. Return to text. NWS State College Case Examples