føhn

Föhn, also spelled föhn wind or foehn wind, is a warm, dry downslope wind that occurs on the leeside of a mountain range after air has risen over the windward slope. The term is most closely associated with the Alps but analogous winds occur in other ranges, such as the Chinook in North America, the Zonda in the Andes, and other regional names.

Mechanism: moist air is forced to rise on the windward side, where it cools and condenses moisture, often producing precipitation. The release of latent heat partially offsets cooling, and by the time the air reaches the crest it may be near saturation. As it descends on the leeside, the air is compressed and warms adiabatically, becoming unusually warm and dry. Relative humidity drops and skies often clear. Föhn events are typically linked to specific synoptic setups with strong prevailing winds and an inversion layer on the windward side.

Characteristics and effects: temperatures can rise by several degrees per 1000 meters of descent, and strong gusts are common. The wind can rapidly melt snow, influence local microclimates, and affect agriculture and viticulture in valleys. In mountainous regions, föhn winds can contribute to rapid weather changes and, in some cases, to avalanche activity due to sudden warming and altered snow structure.

Etymology: the word originates from Swiss German föhn, referring to this warm, drying wind phenomenon; English usage often uses the term foehn wind.