I witnessed the phenomenon of orographic lifting on an almost daily basis during the warm summer days in California's Central Valley. East of our foothill home, large cumulonimbus clouds would form every afternoon as the warm valley air rose upslope on the west side of the Sierra Nevada mountains. Throughout the afternoon, the cumulonimbus clouds would form the telltale anvil head, signaling the development of a thunderstorm. The early evenings would sometimes bring lightning, showers, and hail. The warm valley air had been lifted, created instability in the atmosphere, and caused thunderstorms, which squeezed the moisture from the air.
Rain Shadow Effect
As a parcel of air rises up the windward side of a mountain range, it has its moisture squeezed out. Thus, when the air begins to descend the leeward side of the mountain, it is dry. As the cool air descends, it warms and expands, reducing its possibility of precipitation. This is known as the rain shadow effect and is the primary cause of leeward deserts of mountain ranges, such as California's Death Valley.
Orographic lifting is a fascinating process that keeps the windward sides of mountain ranges moist and filled with vegetation but the leeward sides dry and barren.
