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foehn effect
The foehn effect. When warm, moist air (1) crosses a mountain range, it cools as it climbs the windward side and deposits most of its moisture as rain (2). On its descent on the leeward side of the range, the now drier air heats up much more rapidly (3), giving rise to hot, dry weather downwind.

A warm, dry wind coming down the leeward slopes of mountains due to air having lost its moisture while ascending the windward slope, then warming on its descent. See also chinook.

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