It has been snowing in the western Alps since Saturday and the snow line will drop further in the coming hours. A significant amount of snow will fall in the western Alps and the areas around the Ortler massif until Wednesday. After a dry and mild October month a good storm finally hit the Alps.
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The jet stream that went around the Alps with a large arc for a long time has found its way back to the Alps. The result is a very complex system of low-pressure areas around the British Isles. Fronts find their way to the Alps with west to southwestern currents at first. The snow line was still quite high at the start (2800 meters) but is now dropping towards 2000 meters and will eventually fluctuate somewhere between 1600 and 2000 meters.
In addition, the temperature in the free atmosphere is not exactly low. The zero degree level fluctuates around 2100 meters. Still, I get reports of a snow line that is already quite low locally. A typical example is the valley of Courmayeur, where the snow line has already fallen (on Sunday morning 3 November) towards the 1500 meters. It is already wintry in Courmayeur around Pra Neyron at an altitude of 1850 meters.
At the same time, the snow line on the other side of Mont Blanc is still around 2400 meters and higher. It is raining at the hôtel du Montenvers (located at 1913 meters) this morning and you can see that the snow line is considerably higher.
Heavy snowfall in Courmayeur and a relatively high snow line in Chamonix. That may sound strange at first glance. Certainly because Chamonix is located more to the west and the jet stream is turning west. A brief explanation: On the approach of a storm, the current in the Alps became southwest. In such a situation, the fronts mainly clash on the south side of Mont Blanc, while on the north side they only gently touch the Mont Blanc massif. The trim is therefore much stronger on the south side because the Mont Blanc forms an immense wall. Precisely because of the enormous peaks in the massif, the front on the south side is stopped and forced to rise very fast. This results in a great drop in temperature (orographic cooling we call it), which makes it snow much more heavily in Courmayeur at the time of writing than in Chamonix.
The first signs of storm Amélie were seen on Saturday. She really kicked in in the night to Sunday. A gust of 163 km/h was measured at the French coast and more than 140000 households were temporarily without power (source).
Amélie was primarily responsible for snow on the southern side of the Alps but is now slowly moving into the Alps. The result is that the current, especially in the western Alps, becomes more westerly and we see the air temperature drop from east to west in the coming hours.
A lot of snow falls in the high alpine of the western Alps up to and including Monday. In particular, around the Mont Blanc massif and the Ortler massif (Stelvio, Sulden, Bormio) it is snowing heavily. As mentioned, the snow line drops towards 1500-2000 meters.
I expect the following snow quantities above 2400 meters up to and including Monday evening:
A new storm depression will move to the Alps from the southwest in the course of Monday. This provides a lot of snow in the French Southern Alps at first and for the southern side of the Alps on Tuesday. In addition, there is a chance that as this Genoa-low moves farther to the east, the current will become north and (parts of) the northern side of the Alps will also get snow. With the storm of Tuesday / Wednesday there will be areas in the high alpine of the Alps where more than a meter of snow has fallen. But due to the continuous wind, the differences will be large.
There's more coming up after the snowfall on Tuesday and Wednesda. According to the most recent calculations, the jet stream will continue to come from the west and we have a good chance of an intense storm cycle again with lots of snow from Thursday to next weekend.
Stay stoked, Morris