sec t ion
geography
ClassDate
North America Geography & History SEC TION 1. 3
Name
Use with North America Geography & History, Section 1.3, in your textbook.
GeoActivity
Go to Interactive Whiteboard GeoActivities at
myNGconnect.com to complete this activity online.
1 . 3 W es t ern M oun tains and D eser t s
Illustrate the Rain Shadow Effect
Rain Shadow Effect
Mountains are an important factor in determining whether a region has a
moist or dry climate. This is especially true of coastal mountain ranges like
those along the western coast of North America.
Moisture from the Ocean When sweeping winds blow east from the Pacific
Ocean, they carry warm, moist air. When the air reaches the mountains, it
is forced up the windward slope—the side near the water. As the air rises, it
cools. Because cool air can hold less moisture than warm air, the water vapor
in the air condenses. It falls as rain or snow.
What Causes a Rain Shadow? By the time the air reaches the other side
of the mountain, it is cool and dry. The air sinks down on the land side and
warms up, but it is very dry. As a result, little rain or snow falls in this region.
That is because it lies in the rain shadow behind the mountain range. The
rain shadow effect helps explain why there are deserts in the southwestern
United States and northern Mexico.
1.Describe the Rain Shadow Effect Supply labels in the diagram at right to
explain what happens when a rain shadow is created. Use arrows to show
how the air moves up and down each side of the mountain range. Label
what happens at each step.
b. d. a. Winds blow east
from the Pacific.
e. 3.Draw Conclusions The Coast Ranges and the Cascade Range are
mountain ranges that run along the Pacific coast in Washington and
Oregon. The average annual precipitation (rain and snow) is given below
for five cities in those states. Which cities are in the rain shadow? How
do you know?
• Eugene, OR: 51 inches
• Medford, OR: 18 inches
• Spokane, WA: 17 inches
• Yakima, WA: 8 inches
• Seattle, WA: 38 inches
© NGSP & HB
2.Make Predictions On which side of a mountain range—windward or
landward—would you expect to find thick forests? Why?
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