Orographic lift occurs when an air mass is forced from a low elevation to a higher elevation as it moves over rising terrain. Orography is the study of the topographic relief of mountains. As the air mass gains altitude it quickly cools down adiabatically, which can raise the relative humidity to 100% and create clouds and, under the right conditions, precipitation.
Orographic lifting can have a number of effects, including precipitation, rain shadowing, leeward winds, and associated clouds.