https://lsintspl3.wgbh.org/en-us/lesson/buac20-il-mountainshadow/?as_guest=True&next=https://rmpbs.pbslearningmedia.org/resource/buac20-68-sci-ess-mountainshadow-il/mountains-and-rain-shadows-interactive-lesson/

This image was taken from a satellite that is looking down on the Cascade Mountain Range and Mount Hood from above.

This picture is in natural color, which means that it shows the colors of the region similar to how they appear in the real world. The colors can provide clues as to what the climate might be like (on either side of the mountain range).

Use this image and the next to answer question #5.

How different can climate conditions be on either side of a mountain? Let’s look at the data for two towns that are on either side of the Cascade Mountain Range.

Packwood is a town on the west side of the Cascade Mountains in the state of Washington in the Pacific Northwest region of the United States. At a similar elevation and latitude on the east side is Yakima, WA. The distance between Packwood and Yakima is about 55 miles.

All around the world there are mountain ranges that have a region that is much drier on one side—like the mountain range shown in this diagram.  What causes this to happen?

To understand how a mountain range affects the climate nearby, first think about where the moisture in the atmosphere comes from.

When wind blows over the ocean or other source of water, the air picks up water vapor as water evaporates from the surface of the body of water.

In this way, the wind carries off moisture as it moves away from the body of water.

Large-scale winds that blow predominantly in the same general direction over a particular region during a given period of time are called prevailing winds. These winds can carry water vapor a long distance from water sources.

In some places these prevailing winds encounter a landform, like the mountain range in this illustration.

The side of the mountain range facing the prevailing wind is called the windward side. The side facing away from the prevailing wind is the leeward side.

As air carrying moisture moves toward a mountain range, the slope of the mountain range forces the air upward.

The diagram on the left illustrates how the air pressure higher up in the atmosphere is lower because fewer molecules push down from above. Therefore, as the moisture-filled air rises, it expands as the air pressure decreases. As the molecules in the air move further apart, they lose energy and slow down, which lowers the temperature.

Eventually, the droplets become large enough that gravity causes them to fall to Earth as rain, sleet or snow.

With most of its moisture removed due to precipitation, the air now passes over the summit of the mountain range and begins to descend on the other side.

At lower levels in the atmosphere, the air pressure is greater because more molecules in the air press down from above.

As the air descends, the molecules that make up air are forced closer together and rapidly gain energy, increasing the temperature. The air—by now very dry—becomes warmer as it continues to move down the mountain range.

The lack of

moisture and of rain on the leeward side of a mountain range results in a "rain shadow"—a patch of land that is very warm and dry. Many deserts around the world result from the rain shadow effect

Another example of a rain shadow effect. This mountain is in the Andes Mountains in Bolivia in South America. Look at the satelite image of the same place below.