Rain shadow
A rain shadow is a dry region on the surface of earth that (with respect to the prevailing wind direction) is leeward or behind a mountain. A rain shadow area is dry because, as moist air masses rise to top a mountain range or large mountain, the air cools and water vapor condenses as rain, falling on the windward side or top of the mountain. This process is called [[Precipitation (meteorology)| orographic precipitation]]. The effect of the process is the creation, on the leeward side, of an area of descending dry and warming air, and a region that is quite arid.Good examples (in the United States; rain shadows occur worldwide) are in the deserts of the Basin and Range Province, or the dry areas east of the Cascade Mountains of Oregon and Washington State. The apty-named Death Valley is another good American example; it is behind both the Coastal Range of California and the Sierra Nevada range, and is one of the driest places on Planet Earth.