A mild, dry, extremely turbulent westerly wind on the eastern slopes of the Rocky Mountains and closely adjoining plains. The term is an Indian word which means “snow-eater,” appropriately applied because of the great effectiveness with which this wind reduces a snow cover by melting or by sublimation. The chinook is a particular instance of a type of wind known as a foehn wind. Foehn winds, initially studied in the Alps, refer to relatively warm, rather dry currents descending the lee slope of any substantial mountain barrier. The dryness is an indirect result of the condensation and precipitation of water from the air during its previous ascent of the windward slope of the mountain range. The warmth is attributable to adiabatic compression, turbulent mixing with potentially warmer air, and the previous release of latent heat of condensation in the air mass and to the turbulent mixing of the surface air with the air of greater heat content aloft. In winter the chinook wind sometimes impinges upon much colder stagnant polar air along a sharp front located in the foothills of the Rocky Mountains or on the adjacent plain. Small horizontal oscillations of this front have been known to produce several abrupt temperature rises and falls of as much as 45–54°F (25–30°C) at a given location over a period of a few hours. Damaging winds sometimes occur as gravity waves, which are triggered along the interface between the two air masses. Front Precipitation (meteorology) Wind