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EARTH SCIENCE REGENTS NAME___________________ PERIOD _____ Station Models Tutorial Copyright 1996 by S. Kluge When you watch a weather report, the meteorologist describes the condition of the atmosphere at the present time, and makes a prediction about the future conditions that will exist in the atmosphere in the next 12 to 24 hours, and even for the next 5 days. Meteorologists get the data they need from synoptic weather maps maps that show weather conditions from a number of weather stations around the country. Individual weather stations report current conditions which are encoded on the map. This quick lab exercise will familiarize you with the information and method of encoding information on weather maps. 1. Make a list of all the conditions a meteorologist would include in a careful description of the current weather conditions. I’ve given you an easy one for a start. _______________________ Temperature Cloud Cover _____________ Visibility ________________ Dewpoint _______________ precipitation amount ______ _______________________ Wind Speed _____________ barometric trend (change in atmospheric pressure)____________ Wind Direction ___________ Current Atmospheric Pressure _______________________ 2. Read Topics 13 and 14 on pages 509 and 510 in your text, and the “Weather Station Model” chart in the ESRT. Then, label what each feature on the station model drawn below represents: 82 10 65 003 + 34 / .1 3. There are probably a few things you thought might be included in the station model that aren’t included here, and there are probably a few things here that you never thought of. 4. Use your text index to find, read about, and define the following terms: dew point: The temperature at which air is saturated with water vapor. __________________________ ___________________________________________________________________________________ relative humidity: The extent to which air is saturated with water vapor; it is expressed as a percent. ___ ___________________________________________________________________________________ 5. Find the long, narrow, vertical chart on your reference tables labeled “Pressure”. What is the highest pressure (in millibars) labeled on that chart? ___1041 mb_______ What is the lowest pressure, in millibars, labeled on the chart?__965 mb___________ The two pressures above are the approximate high and low limits of atmospheric air pressures that are observed at the earth’s surface. Meteorologists take advantage of the limited range of observed pressures to encode them on the weather map. Station Models, page 2 of 4 The following explains how barometric pressures are encoded on a weather map. Example 1: 1013.7 mb a. Drop the decimal point ex. 10137 b. Report the last 3 digits ex. 137 Example 2: 989.6 mb a. 9896 6. Try encoding these: b. 896 1022.7 = ____227_________ 998.0 = __980_________ Meteorologists encode the pressures that they report on their station models. The following explains how barometric pressures are decoded when reading a weather map: Example 1: 146 a. Replace the decimal point ex. 14.6 b. Place a “9”, then a “10”, in front of the coded number ex. 914.6 1014.6 c. Determine which of the 2 decoded pressures falls within the normal range of pressures at the earth’s surface (960 - 1040 mb). ex. Example 2: 914.6 is below the normal range, so 146 is the code for atmospheric pressure of 1014.6 mb. Too High! 972 a. 97.2 b. 997.2 7. Try these: 127 = __1012.7mb______ ___1000.1mb__________ or 1097.2 c. 997.2 865 = __986.5mb________ or 1097.2 001 = 8. What is the decoded pressure on the station model drawn on page 1 of this lab? ____1000.3mb_________ Good forecasting requires us to know what the barometer has been doing lately (rising, falling, or holding steady), and where the barometer is heading. This barometric pressure information is indicated as follows on the station model: Example + 34 / The “+” means that the pressure is higher now than it was 3 hours ago. The “34” is code for 3.4 mb. This is how much higher the barometer is now than it was 3 hours ago. The “/” means the barometer is still rising now. It is called the barometric trend. Example - 27 \ The “-” means that the pressure is lower now than it was 3 hours ago. The “27” is code for 2.7 mb. This is how much lower the barometer is now than it was 3 hours ago. The “\” means the barometer is still falling now. Example - 31 The “-” means that the pressure is lower now than it was 3 hours ago. The “31” is code for 3.1 mb. This is how much lower the barometer is now than it was 3 hours ago. The “ - ” means the barometer is holding steady now. Station Models, page 3 of 4 9. An Example: Wind direction? ____Northwest_____________ Wind speed? _____15 Knots_____________ What is the temperature? __35___oF ___2____ o C (use the conversion chart in the reference tables) What is the dew point? ____10__oF 13___ oC ____- What is the present barometer reading at this station?___1019.9 mb_________ Is the barometer higher or lower than it was 3 hours ago? __higher__________ How much has the barometer changed in the last three hours?___3.1 mb________ What was the barometer reading 3 hours ago? __1016.8 mb _________ What is the barometer doing NOW (rising or falling)?___rising__________ 10. Another Example : Wind direction? __Southeast_____________ Wind speed? ___25 Knots_____________ What is the temperature? __84_____oF __29__ o C (use the conversion chart in the reference tables) What is the dew point? ___68____oF o C ____20__ What is the present barometer reading at this station?____999.3 mb________ Is the barometer higher or lower than it was 3 hours ago? ___lower_________ How much has the barometer changed in the last three hours?__1.1 mb_________ What was the barometer reading 3 hours ago? __1000.4 mb_________ What is the barometric trend here?_____Pressure has dropped in the last 3 hours, but it is currently increasing What is the relative humidity of the air at this station? ____60%60%___ (This is a little tricky - you'll need to use both charts on page 12 of the ESRT. Use the Dewpoint Chart first, and work 'backwards' to find the difference between the dry bulb and the wet bulb. Use that information to find the RH on the Relative Humidity chart) 11. Draw a station model below indicating the following conditions. Overcast skies, Temperature is 78oF, dew point of 74oF, barometer 3 hours ago 1003.6 mb, now 1000.1mb and falling. wind NNE* at 20 knots, visibility one half mile, light rain falling. Enter only the information that is used on an official station model (for instance, record only the numerical part of the temperature - not the °F label!) 78 • 1/2 74 Station Models, page 4 of 4 *Remember: Winds are named for where they come from. 001 -35 \ The image to the left is part of an actual synoptic weather map of the US from 11 March, 2003. It shows Texas and New Mexico, and parts of the surrounding states, Mexico, and the Gulf of Mexico. The stations have been labeled A - G for the purposes of this exercise. Which station is reporting the lowest temperature? __D________What is that temperature?___55 °F______ Which station is reporting the highest dewpoint?____G____ What is that dewpoint?___68_°F _____ Which station is reporting the highest air pressure?___F_____ What is that pressure?___1012.3 mb______ Which station is reporting the lowest air pressure?____D____ What is that pressure?__1007.6 mb_______ Which station probably has the highest relative humidity?___F______How do you know?_____See below - Cloud Cover (100% or overcast) - The difference between the air temperature (also known as the dry bulb) and dewpoint is small. Since the dewpoint is almost equal to the temperature (or “dry bulb”) with a difference of only 1 °F, then the air is nearly saturated with water vapor. Where is the air at that station coming from?_____Southeast (Gulf of Mexico)__________ Which stations are probably in the driest air mass?__A or B_______How do you know?____See below_______________ Where is the air at that station coming from?_____South / The dry mountains of Mexico.__________ Consider the answers to the last 4 questions above, and make a clear, thoughtful statement about relative humidity of air masses that form over water and air masses that form over land. The air originating from the ocean is arriving at station F. This station has a high moisture content as it is dominated by mT air mass characteristics. In contrast, the air in middle Texas (station A) was relatively dry, since it is lacking a source of moisture relatively nearby. ________________________________ ___________________________________________________________________________________ Station G air temperature = 71°F (__22_____° C); dewpoint = 68°F (° ___20_____°C); RH = 88% Station F air temperature = _66__°F (__19_____° C); dewpoint = _65__°F (° _18_______°C); RH = 91% Station A air temperature = _61__°F (__16_____° C); dewpoint = _15__°F (° __-10_____°C); RH = Station Models, page 5 of 4 Station B air temperature = _65__°F (__18_____° C); dewpoint = _20__°F (° __-7______°C); RH =