The winter conditions in the Northern Alps will be hit hard from today by the incoming southern Föhn. Especially in Switzerland, the temperatures in the typical föhn valleys will rise considerably. At the same time, it starts to snow in more and more places in the Southern Alps in the course of the evening.
Today, a Südföhn situation is developing in the Northern Alps due to the strong south-westerly current. High pressure on the south side of the Alps and an increasing influence of the low pressure area above Great Britain means that the North-South pressure difference can reach up to 13 hPa, as can be seen in the föhndiagram of Meteocentrale. This increase in the pressure gradient is a good indicator for föhn, where a positive pressure difference produces Südföhn in the Northern Alps and a negative pressure difference Nordföhn in the Southern Alps. In the Föhn chart above, Lugano (south) and Zürich (north) are used. Other common locations for the Föhn in the Eastern Alps is the pressure difference between Bozen (south) and Innsbruck (north).
Outside the typical Föhn valleys, the cold air can maintain itself a little better, but especially in Switzerland, the temperatures in the typical Föhn valleys (like Adelboden) can rise to well above 10 degrees. Even locally 15 degrees could be possible. In Austria too, temperatures above 10 degrees will be measured locally today and on a large scale tomorrow and the day after tomorrow.
With such a Föhn situation, strong gusts of wind must of course be taken into account. The 10-meter wind forecast above clearly shows that the Föhn will also be strong in many north-south valleys (Rhine Valley, Reusstal, etc.).
At the same time, the Southern Alps will have to deal with fresh snow in the course of the evening. Today, especially in the eastern Southern Alps, it's still a beautiful day, but further west, more and more clouds are coming in. In the western Southern Alps it can start to snow as early as the late afternoon. The snowfall continues in large parts of the Southern Alps (with only short dry intervals) until Friday. On Friday in particular, precipitation intensifies due to an approaching low-pressure core from the west above the Bay of Biscay.
Until tomorrow afternoon, it is mainly Ticino and Valchiavenna that benefit from the snowfall with 10 to 20 centimeters of fresh snow above 800 to 1200 meters, but the French Southern Alps can also get about 10 centimeters of snow above 1000 to 1200 meters. In the afternoon the intensity of the snowfall temporarily decreases, but in the course of the evening it can snow again more heavily. This snowfall does go hand in hand with the warmer air entering, so that the snow line will rise in the course of Friday. During the peak of the precipitation, the snow line rises above 1500 meters in many parts of the Southern Alps, but the sheltered inner-alpine valleys can benefit from a lower snow line for a little longer due to precipitation cooling. This all depends on the intensity of the precipitation and the strength of the wind.
In total, more than 30 centimeters of snow can fall on a large scale, locally as much as half a meter, especially in Lombardy and the higher parts of the Julian Alps. The models do not fully agree on the precise amounts of precipitation. The uncertainty is somewhat greater for the Dolomites in particular, with the southern Dolomites having the greatest chance of amounts of around 30 centimeters.
But what about that snow in the Western and Northern Alps on the forecast map? In the course of tomorrow evening a south-westerly current will also bring some precipitation to the Western Alps. The snow line can temporarily be quite high here (> 1600m), but I don't expect much more than 10 centimeters in the French Alps in the night from Thursday to Friday.
On Friday, the Föhn situation in the Northern Alps will quickly collapse with an approaching cold front from the west. Under the influence of the powerful low-pressure area above the North Sea, colder and moist air is supplied, so that it can also start snowing in the Western and Northern Alps with a decreasing snow line. In a short time 10 to 30 centimeters of snow is possible. In Austria, the cold front follows in the night to Saturday with a snow line that drops from about 1200 meters into the valleys in the course of the snowfall. Here I expect a maximum of 10 to 15 centimeters of snow. How it will then proceed is still somewhat uncertain. After the cold front, it seems to clear up temporarily on Saturday, but new precipitation soon follows from the west.
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