Almwind

The Almwind (also spelled Alm Wind) is a local mountain wind occurring in the Alpine regions of Central Europe, particularly in Austria, southern Germany, and Switzerland. It is a valley breeze that develops during the daytime as a result of differential heating between mountain slopes and the surrounding air. The term “Alm” refers to mountain pastures or high Alpine meadows, hence the name Almwind, meaning “wind of the Alpine meadows.”

Nature and Classification

The Almwind is part of a mountain–valley wind system, which includes two complementary daily wind movements:

1. Valley Breeze (Daytime Wind) – Known as the Almwind, it blows up the slopes during the day.
2. Mountain Breeze (Night Wind) – Known as the Bergwind, it blows down the slopes at night.

These winds are caused by thermal differences between elevated slopes and the valley floor and are typical of mountainous terrain under calm, clear weather conditions.

Mechanism of Formation

The Almwind forms through local convection driven by solar heating:

1. Morning Heating:
   • As the Sun rises, mountain slopes receive direct sunlight and warm more rapidly than the valley floor.
   • The air above the slopes becomes warmer and lighter (less dense) than the surrounding air.
2. Upslope Flow:
   • The warm air begins to rise along the slopes.
   • Cooler, denser air from the valley moves upward to replace it, creating an upslope or valley breeze — the Almwind.
3. Peak Development:
   • The Almwind is strongest during midday to afternoon, when temperature differences between the slopes and valley floor are greatest.
4. Evening Reversal:
   • After sunset, the slopes cool rapidly by radiation.
   • The air above becomes denser and flows downhill into the valley as the Bergwind (mountain wind).

Characteristics of the Almwind

The Almwind usually extends up to a few hundred metres above the ground and is confined to valleys and lower mountain slopes.

Climatic and Environmental Significance

1. Local Weather Regulation:
   • The Almwind contributes to the diurnal circulation of air in mountainous areas, maintaining local temperature balance.
2. Moisture and Cloud Formation:
   • As the warm, moist air rises, it can cool and condense, forming cumulus clouds near ridge tops in the afternoon.
   • This can occasionally lead to localized thunderstorms in the high Alps.
3. Agricultural Importance:
   • The Almwind helps ventilate Alpine meadows (Almen), aiding in temperature regulation and evaporation, which is beneficial for grazing livestock and vegetation.
4. Impact on Air Quality:
   • It promotes vertical mixing of air, dispersing pollutants and refreshing the mountain atmosphere.