There are great dynamics in the weather maps. It's autumn in the atmosphere, and I can see that in the details of the maps. The details keep on changing, but the outline is clear: heavy snowfall. But the devil is in the details for parts of the Alps. In this forecast:
The weather in the Alps in calm today. The sun is shining pretty much everywhere and it will be a lovely day, except in Austria. They are already dealing with clouds that are pushed against the Alps by a current from the north. This results in some light snowfall above 1400-1900 meters on Friday morning, but it definitely isn't much. I expect the sun will come out over there in the afternoon as well.
The image above summarizes the outlook for this weekend. Between high pressure on the Atlantic Ocean (H) and low pressure above Scandinavia (T), cold air is moving south. Once above the Mediterranean, a new little storm depression is formed above the Gulf of Genoa and that means the southern side of the Alps will hit the jackpot. Warm air (red arrow and yellow/orange colors on the second map) comes in east of this storm, while the cold air comes in west of it. The separation between this warm and cold air is indicated on the first map with the blue line and triangles which is called a cold front. The same thing is visible on the second map (the boundary between the blue colors on the left and the yellow/orange colors on the right). We measure this temperature at an altitude of 1400 meters. The precipitation will come down as snow in the blue colors and more often as rain in the orange colors.
You'll see a lot of clouds over the Alps when you look at the third map. A large part of the clouds is located on the right of the cold air. These clouds are in warm air, which will result in rain at high altitude. And because that warm air has some difficulties moving east, we'll probably mostly see rain or a strong Föhn in the eastern regions of the Alps. This is the big picture, now let's have a look at the details.
An emerging wind from the southwest will hit the Alps on Saturday. It starts to snow in the French southern Alps and on the southern side of the Alps. The snow line is still very high (around 1900-2200 meters). It might only drop already just south of the Ecrins. It's pretty warm on the Austrian glaciers due to the Föhn, with some room for the sun and a strong wind.
The precipitation on the south side of the Alps will intensify in the night to Sunday. It will snow heavily in the French southern Alps and the resorts on the border between Italy and Switzerland from Sunday morning. This will stretch past the Ortler and the snow line will drop from 2200 meters to 1500 meters. Except in the Dolomites where the air is warm and the snow line won't really drop. There's still a strong Föhn on the Austrian glaciers that will last till Sunday afternoon. The lifts might close because of that.
The cold front that I previously mentioned approaches the Alps in the course of Sunday morning/around noon. We'll know the exact timing on Sunday. When the cold front hits the Alps, it will not only be snowing on the southern side of the Alps, but it also starts to snow in the French northern Alps and western Switzerland. The snowfall extends to Austria in the night to Monday. The snow line will drop and nestles itself deep in the valleys in the complete Alps. I've picked up 4 crucial moments from our precipitation maps below (go to forecast and click on precipitation to have a look at it).
You'll see the snowfall on the south side of the main alpine ridge on Saturday night. You see that the cold air comes in on Sunday on the second map, and it starts to snow in the French northern Alps. The third map is from Sunday afternoon when the center of gravity is at the border between Italy, Switzerland and Austria, where warm and cold air are battling. The last map is from the night to Monday. It's striking how long it takes the front to move to the east. At the same time, the unstable air will result in new showers for the French Alps.
Sunday is the day when cold and warm air really start battling. The snow limit is high in the warm air and it will rapidly drop in the cold air. This combination creates colorful snow maps for the next three days, but with a high snow line at first. All details can be found here.
According to the calculations, a Genoa-low and this storm depression might bring a lot of snow to the Italian Piedmont after Monday. It's really hard to forecast a Genoa-low and especially a return d'est, but the chances are there and it offers perspective and results in some nice colors on the snow maps. Both our own model and the European model calculate a retour d'est for next week. You can see the pressure map of the ECMWF on the left, with the Genoa depression (white arrow), and on the right the calculated precipitation in our model.
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I'm happy with the snow that's in the forecast, but I'm not going to the Alps this weekend. This snowfall is the first snow for a lot of glaciers (except the ones in Austria). The conditions on the glaciers in France, Switzerland and Italy will definitely improve and the skiing will be good after the weekend.
Stay stoked Morris