Refer to figure.
A Foehn wind is a local warm, dry wind that occurs on the downwind ("leeward") side of a mountain. When moist air is forced to ascend a mountain under stable conditions, it cools adiabatically at the Dry Adiabatic Lapse Rate (DALR) until it becomes saturated, and then cools at the Saturated Adiabatic Lapse Rate (SALR). This process causes precipitation, removing water from the air and lowering the dew point.

As the air descends on the leeward side of the mountain, the cloud base rises, leading to warming at the DALR over a greater vertical distance compared to the cooling at the SALR on the windward side. Consequently, the temperature at the base of the mountain is higher on the leeward side than it was on the windward side. Therefore, on the windward side, low clouds and precipitation are expected, while on the leeward side, clear and turbulent conditions prevail.