What is the term for the dry region on the leeward side of a mountain range?

The dry region on the leeward side of a mountain range is called a rain shadow.

Moist air driven toward a mountain is forced upward in a process called orographic lift. As it rises, it expands and cools; water vapor condenses into clouds and produces rain or snow, mostly on the windward side. After losing much of its moisture, the air descends the opposite slope, where compression warms and dries it.

The term “shadow” describes the mountain’s blocking effect: the range shelters the downwind landscape from moisture. Rain shadows can help create sharply contrasting climates over short distances. The Atacama Desert, for example, is influenced by the Andes, while parts of Patagonia are dry because the Andes block prevailing westerly winds.

A rain shadow is not the same as orographic lift. Lift is the upward movement that helps produce precipitation; the rain shadow is the dry region that develops beyond the range. Descending warm, dry winds are often called föhn winds, or chinook winds in parts of North America.