rain shadow

When prevailing winds encounter a large-scale topographic obstacle, usually a mountain range, the lee side of the obstacle is voided of significant precipitation, becoming a territory where moisture merely shadows the other side. The cooling effect of high elevation causes precipitation on windward slopes, thereby reducing the amount of moisture available to the lee. The White Mountains in east-central California are in the rain shadow of the Sierra Nevada, and the semiarid interior regions of Washington and Oregon are in the rain shadow of the Cascade Mountains.

John Keeble