OROGRAPHIC LIFT: Have you ever noticed one side of a mountain seems to have plentiful trees and vegetation, or a cloud to just one side of the peak? Then on the other side of it, it's dry and arid conditions?
Meteorologist Brittney Merlot explains that when wind is forced from a low elevation to a higher elevation, the air gains altitude and quickly cools down adiabatically, due to less pressure working on the air parcel. This raises the relative humidity and creates clouds and precipitation. This occurs on the windward side of the mountain, which is usually highly vegetated with various plants and trees.
On the other side of the mountain or hill, the air moves down the terrain, and warms from the increased pressure. All of this down-slope work turns into warming temperatures. Giving you a dry and arid area on the leeward side.
In the video above, Merlot breaks it down even more to help you fully understand these processes of an air parcel as it is forced upward and downward due to a mountain or hill.
This phenomenon of orographic lifting can be witnessed on an almost daily basis during the warm summer days in California's Central Valley too. East of the foothills, large cumulonimbus clouds form every afternoon as the warm valley air rises up-slope on the west side of the Sierra Nevada mountains.