PA#9: Update

Last night I already wrote a lot about PA#9 for the northwest Alps, but in this update I go into a bit more detail for the snowfall from tomorrow and beyond.

Past snowfall

The first precipitation phase is behind us. It was quite warm and the snowline was therefore quite high. In this map of the 24-hour snow depth change, we can see that especially Valais and the French Northern Alps around the Mont Blanc massif received quite a bit, but also Aosta and Arlberg. Furthermore, it is also easy to see that especially the lower areas on the alpine edge actually saw more rain. The snowline was around 2,000 metres in many places. In addition, the strong winds in the northern and western Alps were quite noticeable. Where a lot of snow fell, Triebschnee was therefore a problem. For powder, it was soon too warm during the day today. In the valleys, especially on the alpine edge and the Alpine foreland, with west foehn even temperatures of 15 to 18 degrees. Higher up it was also mild.

Updates on upcoming snowfall

From tonight, the second phase that I also wrote about yesterday will follow. The snowfall will continue until Sunday morning, with some respites in between. Thus, snow will temporarily ease in the French Alps and Valais on Friday afternoon. On Sunday, it opens up from the west in more and more places. A summary of what to expect:

Wind Around midnight, winds increase again significantly with highs for the French northern Alps and the Swiss west side tomorrow morning and afternoon. During the afternoon, this wind field also extends further and further eastwards. Large-scale wind gusts of once again 100 to 120 kilometres per hour and maybe even more. Very stormy, which means that many higher lifts will remain closed or will have to close. On Saturday, the wind will decrease again from the west. The northwesterly flow remains strong, but not as bad as on Friday.

Snowline The boundary between cold and warmer air masses is still over the Alps during snowfall. It will not be equally cold everywhere, especially in the French Alps. Because the gradient is so large over a small distance, I cannot rule out surprises. So the snow limits are mainly indications. Small-scale deviations are certainly possible, but a summary on the rough picture:

On the northern side tomorrow (Friday) dropping from 1300 - 1600 metres to 1000 - 1200 metres. In the evening even well below 1000 metres in Switzerland and Austria. Saturday during the day it will warm up again in the French Alps and Valais. Here, the snowline rises again well above 1000 metres. In the rest of Switzerland it may still snow with a low snowline for some time, also in Austria it is colder, but here the intensity of the snowfall decreases on Saturday. For France, the further south, the warmer it is. Near Grenoble and further south, the snowline may even rise again to around 2,000 metres.

Snow amounts Above is an overview of the expected quantities. The centre of gravity is around the French Northern Alps and Valais. Here, 50 - 80 centimetres may fall, locally towards a metre! Up to and including the Arlberg, a decent layer will fall. For the Arlberg itself, it will be around 20 to 40 centimetres, but some extra stau could just provide a bit more. Some of that does fall only from Saturday to Sunday with the passing warm front. After that, with the western flow, the amounts logically decrease again considerably.

Where to go?

In the hotspots of snowfall, you have to deal with a higher snowline and thus heavier snow to quite high. Here you should find the sweet spots with some high treeruns, but check the avalanche reports carefully what is possible and what is not. Tomorrow (Friday) the wind is pretty sure to cause quite a few closed lifts higher up. Too low, you could possibly get some rain on Saturday and too high, so the wind has played a big role. Valais looks more favourable than the French Alps in this respect. Further east, the snowline is thus considerably lower though. In the stau areas from central Switzerland to Engelberg, about half a metre of snow can also fall and it remains quite cold. If you go too far east you are still in the colder air, but also have to settle for a bit less. On Sunday, you should really be looking higher up already (but keep in mind the avalanche danger!), as it gets significantly warmer.

Then warmer

On Sunday follows a warm front with some precipitation especially on the northern edge of the Alps. Temperatures rise again, so the snowline also climbs towards 1300 to 1500 metres again. After that, temperatures temporarily rise further. Due to föhn in the Northern Alps, the zero degree line could reach above 2500 metres on Monday, with temperatures at 1500 metres of around 10 degrees! This is followed by another temporary cooling with snow as well.

Read also:

• What is a Sudden Stratospheric Warming?
• What is an ensemble forecast?
• What are low- and high pressure areas?
• What is a northstau/nordstau?
• What is a southstau/südstau?
• What is föhn?
• What is a retour d'Est?
• What is the jet stream?