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Meteorology
3.4.4.3 The Föhn Wind
Another wind phenomenon is the Föhn Wind, the principle of which is shown
below.
Cool, moist air blows up the mountain side. Initially, the temperature drops by
3°C per 1000 feet. Once the air is saturated, the temperature drops by 1.5°C
per 1000 feet.
Precipitation will fall first as rain and later as snow.
When the air passes over the mountain peak, it is nearly dry and very cold.
As it descends on the other side, the air warms adiabatically by 3°C per 1000
feet.
- Start: 15°C, 83% humidity
- End: 30°C, 12.5% humidity
The final result is nearly dry, warm air (e.g., Norwegian mountains).
3.4.4.4 Rotor winds in the mountains
When flying in mountains, one must be cautious if there are strong winds over
the mountains.
If you approach the
mountain on the windward
side, you will get assistance
to cross, so it's not so bad
here.
Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 258
