Air Masses, Fonts, And Weather Maps


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Lab 9 Air Masses, Fronts, Weather Maps
Reading Lesson 20 is helpful with this lab.
All of the questions are listed here, but they are to be answered in eCampus.
Air Masses and Fronts
Air masses are large bodies of air (over 1,000 miles in diameter) that possess similar
temperature and moisture characteristics throughout. An air mass acquires these
characteristics above an area of land or water known as its source region. When the air
mass sits over a region for several days, or longer, it picks up the distinct temperature
and humidity characteristics of that region. Air masses are classified according to their
source region. Polar (P) air masses originate in high latitudes and are composed of cold
or cool air. (Arctic (A) is very cold air). Tropical (T) air masses originate in low latitudes
and are composed of warm or hot air. An air mass that originates over land is dry and is
referred to as continental (c), and an air mass that originates over oceans is humid and
is classified as maritime (m).
The basic types of air masses are: maritime tropical (mT), continental tropical (cT),
maritime polar (mP), continental polar (cP), and continental arctic (cA).
A front is the area along which two different air masses meet. At a front, the two air
masses have different densities, based on temperature, and do not easily mix. One air
mass is lifted above the other, creating a low pressure zone. If the lifted air is moist,
there will be condensation and precipitation. Winds are common at a front. The greater
the temperature difference between the two air masses, the stronger the winds will be.
Fronts are the main cause of stormy weather.
Along a cold front, the denser, cold air pushes up the warm air, causing the air
pressure to decrease. At the front, there will be a line of rain showers, snow showers, or
thunderstorms with blustery winds. Along a warm front, a warm air mass slides over a
cold air mass. When warm, less dense air moves over the colder, denser air, the
atmosphere is relatively stable.
Figure 1
Refer to Figure 1 to answer questions 1 – 7 and 10.
1. What is name of the air mass for #1 – 8 labeled in Figure 1? (See the basic types
of air masses listed above on page 1.)
a. 1. __________
b. 2. __________
c. 3. __________
d. 4. __________
e. 5. __________
f. 6. __________
g. 7. __________
h. 8. __________
2. What temperature (warm, hot, cool, cold, or very cold) and moisture conditions
(dry or humid) are associated with the following air masses?
a. mT _________and __________
b. cT _________and __________
c. mP_________and __________
d. cP _________and __________
e. cA_________and __________
3. Which air masses have the greatest impact on the west (Pacific) coast of North
America? _________and __________
4. Which air mass originates in the North Atlantic Ocean? ___________
5. Which air mass originates in Mexico? ______________
6. Which air mass originates in southern Canada? ______________
7. Which air masses impact Texas the most? (*hint: there are 3) ________,
_______, and __________
8. What happens to atmospheric pressure (lowers or rises), air temperature (gets
colder or warmer), wind direction, and precipitation as a cold front passes?
Comment on conditions before passage and after passage.
9. How is cold front precipitation different from warm front precipitation?
Figures 2 and 3 are examples of two “real” weather “surface” maps that meteorologists
wouId use to forecast the weather. Identify the different air masses over regions A, B, &
C in Figure 2 below.
10. Region “A” ____________________
11. Region “B” ____________________
12. Region “C” ____________________
Figure 2
13. Identify the types of weather fronts shown in Figure 3 below.
Front “D” ___________________
Front “E” ___________________
Front “F” ___________________
Front “G” ___________________
Figure 3
14. Assume the front in Figure 3 that is moving through the state of Illinois is moving
to the east (or right). Is the temperature in southern Illinois going to get warmer or
colder once the front passes through? ______________
15. Assume the front in Figure 3 that is moving through the state of Pennsylvania
and eastern West Virginia is moving to the east (or right). Is the temperature in
Pennsylvania going to get warmer or colder once the front passes through?
Background: The purpose of this part of the lab is to illustrate the construction and use
of weather maps such as Figures 2 and 3. Every six hours atmospheric data are
collected at approximately 10,000 surface weather stations. Weather data is then
disseminated to national meteorological centers where synoptic-scale (specific time)
maps are generated. Being that each weather station collects data for as many as
eighteen weather characteristics, a method of symbolization must be used to include all
this information on a single weather map. The station model developed by the World
Meteorological Organization (WMO) is the standard format for symbolizing weather
characteristics. The following figure (Figure 4) illustrates the arrangement of data in the
WMO model.
As you will find, each piece of weather information has a specific location in relation to
the station circle. For example, the temperature is always located to the upper left side
of the station circle. Here the temperature is 34°F. Dew point temperature is found to
the lower left of the station. The dew point temperature is 32°F. Units are not plotted
on the station model. The pennant for wind direction is attached to the station on the
side from which direction the wind is blowing (direction is like the points of the
compass: N, NE, E, SW, etc.) Barometric pressure is coded such that you must
add a “9” or “10” in front of the numbers (148) and a decimal between the last two
A good rule: if the number is less than 500, add a “10”, and greater than 500, add
a “9”. In our example: 148 = 1014.8 mb
Figure 4
A table of the symbols used in the WMO model is listed below:
Decode the following two station models.
Temperature = ___________________________
Dew point = _____________________________
Pressure = _______________________________
Present Weather = _________________________
Wind direction = __________________________
Wind speed = _____________________________
Sky covered by clouds = _____________________
Temperature = ___________________________
Dew point = _____________________________
Pressure = _______________________________
Present Weather = _________________________
Wind direction = __________________________
Wind speed = _____________________________
Sky covered by clouds = _____________________
By looking at Figure 5 below:
18. What is the temperature in Dallas? ______
19. What is the wind direction in Dallas? __________
20. Assuming the front that is in Oklahoma and the Texas Panhandle is moving
south and east. Will the temperature get colder or warmer in Texas once it
passes through? _______________
21. How else will the weather in Dallas change as the front approaches and then
once the front passes through? (discuss wind direction, sky cover, any
Figure 5

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