It has been very warm in the Alps in the last few days. The temperatures rose significantly with up to 15 degrees in the valleys and a freezing level that was well above 3000 metres on Wednesday. After some snow today, the high pressure and sunny weather will temporarily return, but on Sunday the first signs of a new weather change will be noticeable. Finally, it's going to snow again in the Southern Alps!
From today onwards it's luckily a lot colder again, which has to do with a north-westerly flow at the moment, which is also bringing snow to most of the valleys. In the Northwest Alps, especially in the Swiss and Vorarlberg stau areas, 10 to 20 centimetres of snow could fall. In Austria and the French Northern Alps, it won't be much more than 5, maybe 10 centimetres. Snow will fall in most valleys, but below 500 metres it will be wet snow or rain.
Behind the front, it clears up quickly in the Northern Alps today. For a large part of the Alps the weekend will be very sunny again. However, the depression you see on the map west of Ireland will approach during the weekend. The core will develop further and will be over England already on Sunday. Due to the increasing pressure gradient between the Southern and Northern Alps, a föhn situation will develop on the northern side during the course of Sunday. The peak of this Südföhn will be in the night from Sunday to Monday. A new precipitation front from the west will clear the föhn in the course of Monday.
While it has already cleared in the Northern Alps, there may still be some snowfall on Saturday, especially in Piedmont. Why is it that it can suddenly snow here? The increasing high pressure will first of all create a strong Nordföhn in Piemonte and Ticino, but on the north side it will create a flow around the Eastern Alps. In the animation of the wind at 1500 meter altitude below you can clearly see why it will snow a bit tonight. The wind is turning clockwise and the east wind is filling the Po Valley with cold air, which then hits this part of the Alps and is forced to rise. Don't expect too much of it, because it's not a moist retour d'est flow from the Mediterranean. It won't be much more than 5 to 10 centimetres at the most.
After a mainly sunny weekend, snow will follow in the night from Sunday to Monday. First of all, it will start snowing in the French Southern Alps because of a south-westerly flow. Later on Monday more snow will follow from the west. With a small area of low pressure over the Mediterranean, it will finally snow again in the Southern Alps. Monday afternoon and evening the precipitation will spread further eastwards.
There are still some differences in the models. The European model leaves Piemonte and Ticino for example largely out of the picture because of this south-westerly flow, while the American model expects more here. Further east, in the Dolomites for example, some 10 to 30 centimetres of snow is possible. I expect most snow in the French Southern Alps with ski areas like Isola and Auron that could get over 40 centimetres with a snowline between 1200 and 1400 metres. Our model overestimates the amounts a bit in my opinion, but shows the distribution of snowfall very well.
After this snowfall, the jet stream will play a major role. In the middle of next week, the jet stream will be zonal and located to the north of the Alps, which means that precipitation will follow from the west, but with the supply of warmer air, the chance of rain will increase considerably. How much and when exactly is still unclear, but especially the Northwest Alps should take into account the occasional rain up to 1500 meters.