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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 =