How does orographic rain occur?

Orographic rain occurs when air is forced up a mountain range by the prevailing winds. As the air rises, it cools and starts to condense, forming clouds which eventually become rain or snow depending on air temperature. Air rises when it encounters the mountain and is forced to flow over the terrain, cooling as it rises. This process is known as orographic uplift. As the air cools it releases its moisture as precipitation. Orographic rainfall can be very localized, with one side of the range receiving much greater precipitation than the other.