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Föhn Effect
From SKYbrary Wiki
| Article Information | ||
|---|---|---|
| Category: | Weather | 
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| Content source: | SKYbrary | 
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| Content control: | EUROCONTROL | 
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| WX | |
|---|---|
| Tag(s) | Weather Phenomena |
Föhn Wind
Definition
A warm dry wind that blows down the lee side of a mountain.
Description
When a large air mass is forced up and over a mountain range (Orographic Lift), clouds and precipitation form as the air rises and cools adiabatically. When the air mass reaches the top of the mountain it has lost a significant amount of its water content and so has a much lower dew point. As the air then begins to descend down the lee slope of the mountain, and the air pressure increases, it warms adiabatically. The resultant wind is dry and warm giving clear conditions at airfields on the lee side of the mountain range. As well as creating a warmer climate, these dry winds can be a cause of wild fires during the summer months which may affect flying operations.
