The Foehn winds is a down slope flow of air that occurs in manyu mountainous areas but is it not caused by the drainage of dense air, It occurs when the prevailing winds in warm, moist air are directed against a mountain. The forced ascent on the windward side, as illustrated in fig given below, usually causes cloud to form, Frequently, precipitation will also occur. During most of this ascent the air is cooled at the moist mountain top, much of the moisture may have been removed. This means that the air at the top has absorbed the latent heat released by the condensation of the moisture it contained. As the air descends the lee slopes, it is warmed at the dry adiabatic rate (100C/km). When it arrives at the bottom of the mountain, the air is warmer than at the same elevation on the windward side, having been heated by the latent heat of condensation. It is also drier because it has lost some of its moisture through condensation and/or precipitation on the windward mountain slope.
The Indians on the lee slopes of the Rockies referred to the wind as snow eater,” encase of the starting way in which large amount of snow could be melted and evaporated by the warmth and dryness of the air.s