Monday is a day of extremes. A super storm called Yves has split off and with a core pressure of 975 hPa, the Alps are subjected to rain, snow, hurricane winds and huge differnces in temperature. And because the storm is so close to the Alps, everything becomes even more extreme. We're about to see pretty much everything that makes the weather so special, from a hurricane-like southern Stau to a northwestern Stau in less than 36 hours. The avalanche danger will rise as well because of the wind, snow and shifting temperatures. In this forecast:
I was still in St. Anton am Arlberg yesterday. The wind was pretty strong on Sunday and it was a bit warmer compared to Saturday, but the humidity in the air kept the temperature low. It started snowing in the afternoon and by the end of the day we were riding powder in the streets of St. Anton am Arlberg. Unfortunately I already knew that the weather would change. I already received messages about rain and a rapidly rising snow line from the west of the Alps. Too bad for all the snow in the valleys that turned into slush today, but there's a solid snow cover above 2000 meters.
The biggest challenge for the snow cover in the northern Alps (including the French northern Alps) today is the wind. A stormy wind with hurricane gusts is blowing in the high alpine and mid-mountain. This wind transports a lot of snow and blows the snow away from the peaks and ridges. It's all caused by a powerful current from the south (red arrow on the map above). This southern current creates an immense Stau on the south side of the main alpine ridge which ensures a lot of snow. There is still a lot of cold air trapped on the south side of the main alpine ridge and the immense Stau also provides the necessary orographic cooling. The snow line can therefore still be found deep in the valleys, but will rise towards the 1200-1800 meters later in the day. The snow line might be found a bit lower in some inner alpine valleys, simply because the cold air can't go anywhere.
You can expect the most snow on the south side of the main alpine ridge in the ski areas south of the Ecrins, Courmayeur, the ski areas around the Ortler, south of the Monte Rosa, Gotthard and Piz Buin. But even in the Italian Piedmont it will be snowing like crazy. You can expect 50-120 cm of fresh snow (and locally even more) above 1800 meters until tonight.
Because storm Yves is moving east, cold air flows into the Alps from the northwest. The Föhn from the south will come to a stop, as is the strong wind and it will start snowing in the northwest of the Alps immediately afterwards. I expect a lot of snow, especially in the French northern Alps, the west and north of Switzerland and the west of Austria.
We'll have to hang in there. The first cold air flows into the Alps by the end of the afternoon and it will extend to the rest of the Alps in the night to Tuesday. A lot of humid air was moved to the north side of the Alps by the Föhn storm and this humid air will get trapped between the incoming cold air and the peaks on the north side of the main alpine ridge. It will snow heavily south of the main alpine ridge on Monday, but I expect a lot of snow on the north side of the main alpine ridge on Tuesday. I expect 15-30 cm (locally 50 cm) from the Haute Savoie to the Arlberg, and the warm air will immediately disappear. The snow line will drop again towards 1000 meters.
Tuesday will be a powder day, but the avalanche danger has become critical. It is still a bit of a guess what is happening in the snow cover right now, but I hope to give you an update tomorrow. If you go out riding tomorrow, check your local avalanche forecast very carefully and ride as defensively as possible!
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We're facing a new storm cycle on Wednesday, but that storm won't be as heavy as the storm we're dealing with now. Another Föhn storm will kick in on Wednesday and that storm will bring snow to the southern and western Alps and it will snow in the northwest of the Alps on Thursday. The cold air will stick around for a while after that.
Stay stoked, Morris