The leeward side of a mountain is not exposed to harsh winds and weather conditions. Mountains push moving air upwards, causing water in the clouds to fall out as rain or snow. Once the air travels over the mountain range, it is free of moisture. As the air descends down the mountain, it warms and expands, giving the leeward side a far drier and warmer climate. Atmospheric pressure decreases with increasing altitude. As air rises it cools until it reaches the adiabatic dew point. At this point, moisture condenses on the windward side of a mountain and precipitates.
The leeward side of a mountain forms from the rain shadow effect. This effect occurs when air cools and expands as it moves from a low elevation to a high elevation. Rain shadows are patches of arid land formed as a result of mountain ranges blocking precipitation. Some of the most expansive deserts formed as a result of rain shadows. Death Valley, a sprawling desert in California and Nevada, is in the rain shadow of the Sierra Nevada mountain range.