We have quite a changeable week ahead of us in the Alps with firstly two polar cold nights, then snowfall for the Western Alps with a slowly rising snowline and a battle between warm and cold air masses close to the Alps. Later in the week, the Southern Alps will get snow and after a temporary föhn period in the Northern Alps, some snow and cooling seems to return here too with a cold front.
It is bitterly cold in the Alps at the moment! The low-pressure core that still provided some snow over the weekend is out of reach of the Alps and is now over Belarus. On its back side, cold air masses are being transported to the Alps. Combined with increasing high-pressure conditions and thus little cloud cover, it can cool particularly strongly during the nights, as was the case last night.
In some locations where temperatures can regularly drop impressively due to the topography, we observed some arctic minimum temperatures last night. On the Glattalp in Switzerland, for instance, it got -35 degrees, but also in official measuring stations in the Engadine and Tyrol, for instance, it cooled down to (well) below -20 degrees. Yet this cold outbreak will not last long, as a low-pressure area over the Atlantic Ocean is going to change things again. Next night, it could get this cold again, but after that temperatures will rise again.
Whereas initially it looked like another exciting situation with plenty of cold still present in the Northern Alps, for Wednesday this 'Luftmassengrenze', a band of precipitation right on the border of cold and warm air masses, is now being calculated a lot further north, bringing considerably milder air north of the Alps.
What remains unchanged, however, is that the Western Alps will get snow first. In the French Southern Alps, a separate advancing low-pressure core will start snowing from the west overnight, but slowly the snowfall will move a bit more towards the French Northern Alps and western Switzerland. The snowline is still fairly low for an extended period, especially in the northern areas down into the valleys, but slowly but surely rises to around 1,500 metres. In most places, around 10 to 20 centimetres of snow will fall, with the French Northern Alps and the Écrins possibly some more.
Behind it follows increasing influence from the more powerful low-pressure area over the Atlantic, which once again pushes moist but also milder air against the Western Alps. During the night from Tuesday to Wednesday, precipitation approaches again with the mild air in the north-west Alps and later also in the rest of the Northern Alps. In particular, the areas on the northern edge of the Alps may experience some rain here. Snow only falls here above 1400 to 1800 metres. The snowline rises in the Western Alps to well above 1500 metres. In the French southern Alps possibly around 2000 metres, but in the latest calculations precipitation amounts remain limited.
The reason why precipitation will most likely remain limited to the alpine edge and not penetrate deeper into the Alps is that an increasing pressure difference between the northern and southern Alps will create a south föhn situation. Inner-Alpine areas will most likely keep it dry with this stormy föhn.
Over the course of Thursday, low pressure over the Mediterranean then brings snow to the southern Alps. First in the French Southern Alps in the morning. Then the precipitation spreads across the rest of the Southern Alps. Due to the south-westerly flow, Piedmont seems to be out of the picture. At the moment, I expect the most snowfall in the southern Dolomites and the areas east of it. The snowfall comes quickly and also leaves again quickly, so accumulations will remain limited. On the north side, we will see a temporary revival of the Südföhn on Thursday, but a cold front looks set to bring cooling and a fresh layer of snow again on Friday. All in all, then, a very changeable week!