Unit 3: Topography & Fire Behavior
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Foehn Winds
The last mechanical effect of topography on weather that we shall discuss is the foehn wind. There are several variations of foehn winds in the Western United States. Instead of dealing with an unstable airmass that produces orographic thunderstorms, here we are concerned with a stable airmass being forced over a mountain range. As this heavy stable air is pushed up on the windward side, it cools, and clouds and precipitation might occur. The air falls on the leeward side and becomes warmer and dryer as it descends. The resulting gravity or foehn winds can be even more pronounced where the air is channeled through saddles or passes. Some localities may experience frequent foehn winds during certain times of year, depending on general weather patterns. Foehn winds take on local names such as the chinooks, which occur in areas east of the continental divide; the Santa Anas of southern California; the Mono and North winds of central and northern California; and the East winds in the Pacific northwest.
Various Foehn Winds in the Western U.S.
