After a cold snap brought early skiing to the Alps, temperatures have swung back the other way. The warm wind from the south, known as the foehn, has brought high winds and warmer temperatures. According to Vincent Devantay of Meteo News, the weather phenomenon brought 163 km/h wind to the top of the 3,500m Jungfraujoch, and 124 km/h wind to the plains of Altdorf in Uri on Monday.
Peak winds have now passed, but temperatures are now markedly higher than last week and are predicted to reach a high of 20 today in Altdorf in Uri (438m), according to Meteo Swiss. Temperatures in some Ski resorts such as Verbier are predicted to exceed 8 degrees today. Not great for the snow.
The warm dry foehn is produced when winds from the Mediterranean, forced up by the Alps, drop their moisture on the southern slopes, leaving warm dry air to pass over the remaining Alpine region and beyond. The phenomenon can quickly drive temperatures up substantially.
Today’s weather shows the phenomenon in action. Heavy rain with relatively low temperatures on the southern side of the Alps in Lugano (12 degrees) and relatively hot dry weather in Altdorf in Uri (20 degrees). These two towns are only 135 km apart.
To predict the foehn, meteorologists look for pressure differences between Lugano and Zurich. If the air pressure in Lugano exceeds that in Zurich by enough then the foehn kicks in. According to Meteocentrale.ch, a pressure difference of 4 hectopascals is enough. The same phenomenon can also occur in the reverse direction.
The word foehn (Föhn in German) is also used to mean hairdryer in French-speaking Switzerland.