Part 2: Fronts

When two unlike air masses meet, a low pressure cell forms due to the mixing. In the northern hemisphere, the

wind will circulate in a counterclockwise direction around the low pressure cell. As a result, cold air moves into

an area containing warm air and warm air will move into an area containing cold air. This results in the

development of a cold and warm front.

Exercise 9.2:

1. Draw the symbols for the following fronts using conventional colors (blue, red and purple)

Cold Front

Exercise 9.3:

Stationary Front

Part 3: Weather Station Model

Weather information is collected at many stations around the world. That data is then plotted on weather

maps in a standard format and code. This format is called a station model. Attachment A at the end of this

lab contains an example station model. When using the station model, it is important to understand data is

placed in a specific location relative to the circle at the center. You need to understand where this data is

in relation to the model in order to properly read the model.

Temperature

1. Looking at the station model for San Francisco, complete the table:

Dew Point Temperature

Pressure* You must include the

initial 9 or 10 in your answer

Pressure Change

Wind Speed

Wind Direction

Total Amount of Clouds

°F

°F

mb

Warm Front

mb

Occluded Front

knots

1028

39

San Francisco 500

33,

278

+2/

2/n3. Identify the source regions for the air masses that affect North America on the map below.

a. Outline the air mass based on temperature (warm = red and cool=blue)

-40°N

30° N

50° N

120% W

Air Masses of North America

North America Albers

Equal Area Projection

110⁰ W-

-100-W-

90°- W

80° W/nName

Lab Nine: Weather Maps and Midlatitude Cyclones

This lab is designed to help you identify the air masses that affect North America and to recognize the fronts

associated with the interaction among these air masses. In addition, you will learn how to read station

model information and to apply this knowledge to hypothetical and real weather maps. While using the

weather maps you will be describing the atmospheric changes that occur within a midlatitude cyclone.

Materials:

Weather map (provided)

Objectives:

Identify air masses that affect North America

Identify low pressure and high pressure on a

weather map

• Identify cold fronts and warm fronts on a

weather map

Part 1: Air Masses

Midlatitude cyclones are the result of unlike air masses meeting. There a several air masses that affect North

America, each with different temperature and moisture characteristics. Air masses get their temperature and

moisture characteristics based on their source regions. For example, air masses that originate over water are

characterized as moist.

2. Fill in the chart with air mass characteristics.

Air Mass

Exercise 9.1:

1. Classify the moisture characteristics (dry or moist) for the following locations:

a. Continental (c)

b. Maritime (m)

Classify the temperature characteristics (cool or warm) for the following locations:

c. Polar (P)

d. Tropical (T)

CP

mP

Red, blue and purple pencils

CT

. Read a weather station model to determine

the weather at a given location.

• Read a weather map to determine how the

weather is changing at various points in a

midlatitude cyclone.

mT

Characteristics

1