8.32 Mountain Weather

8.32.2 Define the Föhn wind.

Fohn – German word derived from the Latin expression “west wind”.

A fohn wind is a warm, dry and gusty wind blowing on the lee side of mountain ranges.

Air ascends up the windward side of the mountain range cooling adiabatically as it rises.

Precipitation must occur on the windward side making the descending air on the lee side much drier.

The cloud base is higher on the lee side because the drier air has a lower dew point, thus the descending air warms for a longer period of time at the DALR.

This results in a net increase in temperature.

8.32.4 In Föhn wind conditions, describe the typical weather:

(a) to windward of the mountain range;

If the Föhn wind carries moist air, the typical weather on the windward side of the mountain range can be cloudy and rainy.

This is because the moist air is forced to rise as it flows over the mountain range, which causes it to cool and condense into clouds.

This can result in precipitation on the windward side of the mountain range, which can be significant in some cases.

(b) above the mountain range;

In a Föhn wind with moist air, the typical weather above the mountain range can be turbulent and unstable, with strong winds and the potential for icing.