Mountain Effect

Take a look at the next three slides and try to answer the following Try to decide why each city has the climate it does. Why does it rain more in certain places than others?

Seattle, WA Boston, MA Las Vegas, NV Memphis, TN Austin, TX Jacksonville, FL Austin, TX

Average Monthly Temperature: Annual Amount of Precipitation: Seattle, WA Average Monthly Temperature: Annual Amount of Precipitation: Inches: 37.07 Days: 155 January April July October 40.9 50.2 65.3 52.7 Annual Snowfall: 11.4''

Jacksonville, FL Average Monthly Temperature: Annual Amount of Precipitation: Inches: 52.34 Days: 116 January April July October 53.1 66.6 81.6 52.3 Annual Snowfall: Trace

Why does it rain more in certain places than others? Mountains near the ocean hold part of the answer. When water evaporates from the ocean, it becomes water vapor in the air. The warm, moist air rises and moves over land.

Figure 7.7 The rain shadow effect is a reduction of rainfall and loss of moisture from the landscape on the side of a mountain facing away from prevailing surface winds. Warm, moist air in onshore winds loses most of its moisture as rain and snow on the windward slopes of a mountain range. This leads to semiarid and arid conditions on the leeward side of the mountain range and the land beyond. The Mojave Desert in the U.S. state of California and Asia’s Gobi Desert are both produced by this effect.

Clouds form that can drop rain or snow on one side of the mountain. Air that meets mountains is forced to go higher, where temperatures are colder. Clouds form that can drop rain or snow on one side of the mountain. This side is called the windward side (closest to the ocean/ wind). Some of the wettest places on Earth are on the windward side of mountains.

After the clouds have dissipated, the air finally crosses to the other side of the mountain. There is usually very little moisture left. Because there is not much moisture left, clouds are not likely to form. This leaves the back side of the mountains often dry and desert-like.

Sierra Nevada Mountain Range The Sierra Nevada Mountains span 400 miles across CA.

The leeward side (western side), however, is a very dry desert region. The windward side (eastern side) of the Sierra Nevada Mountains receive much precipitation and are lush with vegetation. The leeward side (western side), however, is a very dry desert region.

What’s the reason for this? It’s all about the Mountain Effect!

Most of the moisture has already fallen as precipitation. Why is there little moisture left in the air by the time it reaches the leeward side of a mountain? Most of the moisture has already fallen as precipitation.

Why does more rain and snow fall at the top of a mountain than at its base? At the base of a mountain, the air is warmer. The air needs to cool to form clouds that drop precipitation.

If you chose G, you are correct! The air on the leeward (backside) of the mountain is drier than on the windward (front) side of the mountain.

If you chose J, you are correct! The air cools as it rises, causing fog to form.

Notes: Water evaporates from the ocean, and it becomes water vapor. This warm, moist air rises and moves over land. Clouds form that can drop rain or snow on one side of the mountain. The clouds dissipate, and the air crosses to the other side of the mountain. There is usually very little moisture left. *** In your notes, draw a diagram of a mountain and the mountain effect.

Review

If you chose J, you are correct. The land on the leeward side of the mountain receives air with the least amount of moisture, making it hotter.

The correct answer is G. The air is drier at Y than at X. There is more moisture in the air at point X, on the top of the mountain. All of the moisture will be lost on the mountain, making the air at Y drier.