Name
Date
Weather Patterns
■
Class
Adapted Reading and Study
Air Masses and Fronts
Types of Air Masses
(pages 72–79)
(pages 73–74)
Key Concept: Four major types of air masses
influence the weather in North America: maritime
tropical, continental tropical, maritime polar, and
continental polar.
• An air mass is a huge body of air. The air at any
given height in an air mass all has about the same
temperature, humidity, and air pressure.
• A tropical air mass forms in the tropics. A tropical air
mass has warm air. A polar air mass forms near the
poles. A polar air mass has cold air.
• A maritime air mass forms over an ocean. A maritime
air mass has humid air. A continental air mass forms
over land. A continental air mass has dry air.
• A maritime tropical air mass has warm, humid air.
A maritime polar air mass has cool, humid air.
• A continental tropical air mass has hot, dry air.
A continental polar air mass has cold, dry air.
Answer the following questions. Use your textbook and the
ideas above.
1. Circle the letter of each characteristic scientists use to
classify air masses.
a. cloudiness
b. temperature
c. humidity
2. A huge body of air with similar temperature, humidity,
and air pressure at any given height is a(an)
.
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38
Name
Date
Weather Patterns
■
Class
Adapted Reading and Study
3. Complete the table about air masses.
Air Masses
Type of
Air Mass
Temperature
of Air
Humidity of Air
Maritime
tropical
warm
a.
Maritime
polar
b.
humid
Continental
tropical
hot
c.
Continental
polar
d.
dry
How Air Masses Move
(page 75)
• Air masses move. Global winds usually move air
masses from one part of Earth to another.
• The major wind belts over the United States are the
prevailing westerlies. These winds usually push air
masses from west to east across the United States.
• Jet streams also push air masses across the United
States from west to east.
• As air masses move, they bump into each other. A front
is a boundary where two air masses meet. Storms and
other types of weather develop along fronts.
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Weather Patterns
Key Concept: In the continental United States, air
masses are commonly moved by the prevailing
westerlies and jet streams.
Name
Date
Weather Patterns
■
Class
Adapted Reading and Study
Answer the following questions. Use your textbook and the
ideas on page 39.
4. Circle the letter of each wind belt that commonly moves
air masses in the continental United States.
a. prevailing westerlies
b. trade winds
c. prevailing easterlies
5. The boundary where two air masses meet is called
a(an)
.
Types of Fronts
(pages 76–77)
Key Concept: Colliding air masses can form four
types of fronts: cold fronts, warm fronts, stationary
fronts, and occluded fronts.
• A cold front forms when a cold air mass slides under
a warm air mass. Thunderstorms can occur at a
cold front.
• A warm front forms when a warm air mass moves over a
cold air mass. Light rain or snow may fall.
• Sometimes cold and warm air masses meet, but neither
air mass moves over or under the other. The two air
masses face each other in a “standoff.” This is called a
stationary front. A stationary front can bring many days
of clouds and precipitation.
• A warm air mass sometimes is caught between two
cooler air masses. This forms an occluded front.
Occluded means to be cut off. In an occluded front, the
warm air mass is cut off from the ground. The weather
may turn cloudy, and rain or snow may fall.
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40
Name
Date
Weather Patterns
Class
Adapted Reading and Study
■
Answer the following questions. Use your textbook and the
ideas on page 40.
6. Draw a line from the type of front to a description of
how it forms.
Type of Front
How It Forms
cold front
a. A warm air mass moves
over a cold air mass.
warm front
b. A warm air mass moves
between two cold air
masses.
stationary front
c. A cold air mass slides
under a warm air mass.
occluded front
d. Two air masses face
each other in a “standoff.”
7. Circle the letter of the type of front that can result in
thunderstorms.
a. cold front
b. warm front
c. occluded front
8. The pictures show two types of fronts. Circle the letter
of the cold front.
War
Direction
of front
ma
ir
Cold air
Warm air
Cold air
Direction of front
a.
b.
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41
Name
Date
Weather Patterns
■
Class
Adapted Reading and Study
Cyclones and Anticyclones
(pages 78–79)
Key Concept: Cyclones and decreasing air pressure
are associated with clouds, winds, and precipitation.
• A cyclone is a swirling center of low air pressure. The
winds in a cyclone spiral around a center. In a cyclone,
winds spiral inward towards the low-pressure center.
• The Coriolis effect makes winds spin counterclockwise
in a Northern Hemisphere cyclone.
• Air spins upward in a cyclone. The result is clouds, wind,
and precipitation.
• Cyclones play a large part in the weather of the
United States.
Answer the following question. Use your textbook and the
ideas above.
9. Circle the letter of what kind of weather a cyclone
brings.
a. clear, dry weather
b. wind and precipitation
c. sunny and hot
Key Concept: The descending air in an anticyclone
generally causes dry, clear weather.
• An anticyclone is a high-pressure center of dry air.
An anticyclone is the opposite of a cyclone. In an
anticyclone, winds spiral outward away from the
high-pressure center.
• The Coriolis effect makes winds spin clockwise in a
Northern Hemisphere anticyclone.
• The air spins down in an anticyclone. The result is dry,
clear weather.
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42
Name
Date
Weather Patterns
■
Class
Adapted Reading and Study
Answer the following questions. Use your textbook and the
ideas on page 42.
10. Circle the letter of the kind of weather an anticyclone
brings.
a. dry, clear weather
b. hot, rainy weather
c. thunderstorms
11. The pictures show a cyclone and an anticyclone.
Circle the letter of the anticyclone.
L
H
a.
b.
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43