Foehn is a term often brandished by skiers but seldom used correctly.
The Foehn, or Föhn effect occurs over mountain ranges around the world but the phrase was originally coined in reference to winds that blow over the Alps. Pronounced fø-n, the word is derived from the Latin word favonius, meaning spring breezes.
In short the phenomenon happens when moist air is generated over a large body of water and blown inland. These fast moving systems, heavy with moisture are forced to ascend to a higher, cooler altitude when they reach mountain ranges. The damp air cools releases it’s moisture via precipitation, in summer this manifests in sudden and sustained rainfall and in winter in the form of heavy snowfall.
Whilst this sounds like good news for skiers, there is also a darker side to the weather system. Once the air has deposited it’s moisture on the rise over the mountains it descends on the other side of the mountain, or the lee, the air warms. This warm, dry air can be quite pleasant in summer, but in the winter, particularly in the second half of the season, it causes havoc in resorts that lie in the lee. The fast moving dry air is responsible for rapid temperature rise, melting snowfall at a ferocious rate, casing snow conditions to deteriorate and the avalanche risk to increase rapidly.
Foehn winds on the downward side of the valley are known for their strong warm gusts and are said to cause madness - although this has never been proven!
View the Ski Club’s in depth weather forecasts and snow reports.
These types of storms explain how some resorts in the Alps can see increased snowfall whilst resorts on the Lee side of a mountain, in the shadow of the Foehn, see none of the benefits of a Foehn wind. Foehn winds are typically blown in from the Atlantic and over France or up the Mediterranean where they rise sharply over the Alps.
Earlier this season a Foehn and was in part responsible for blocking off the resort of Zermatt from the outside world. Following a strong retour d’est at the start of the season the warm winds caused havoc with the snowpack resulting in avalanches over major transport links. Roads were at a standstill for one of the busiest transfer days of the season.