Surprise PA#9 for the Northwestern Alps!

What a surprise today! After a lot of nasty weather maps over the past few days, we suddenly woke up this morning to new winter chances. Snow instead of rain! I do want to add right away that it doesn’t mean it’s suddenly party mood everywhere, small changes are still possible, but at least the developments are a lot more positive. It is high time to see what the models have shown today AND it is time for PA#9, because with this lower snowline, more is possible!

In this weather report

• First snow phase underway
• Temporarily calmer
• More snow tomorrow night - what does the snowline do?
• Wind remains an issue!

First snow phase underway

The first snow phase is currently underway. Most of it will fall in the French Northern Alps and western Switzerland, around 30 to 50 centimetres. In the process, the snowline already rose to around 1600-1800 metres, locally to around or even above 2000 metres. It was also already very very windy, especially in the exposed areas for these westerlies. On a large scale with wind gusts of 80 to 100 kilometres per hour. On the Pilatus, Säntis, Diavolezza, Jungfraujoch and the Hoher Kasten, wind gusts of 120 to as much as 140 kilometres per hour were measured. It is then of course no surprise that the avalanche risk also rose again. Due to the greatest amounts it’s the highest in western Valais and the French Northern Alps, but also elswhere it’s important to check the full avalanche bulletins. The snow is falling on unfavourable old snow and with the wind involved, wind slabs are of course also a problem. So there will be some powder to score in this region tomorrow, but the choices are very limited due to the conditions. Too low and it has rained, too high and it is too tricky with the avalanche risk.

Temporarily calmer

Tomorrow morning (Thursday), the intensity of the precipitation decreases again for a while and the sun gets some more space during the day. On the northern side of the Alps it will continue to snow a bit longer. Snowline here too will remain at around 1,600 to 1,900 metres, but precipitation will be limited mainly to the northern alpine rim. Further south in Austria too, it may clear up widely during the day.

More snow from tomorrow evening

So far barely any changes compared to what I wrote yesterday, but the snow episode from tomorrow night (Thursday on Friday) through Saturday has thus changed rigorously in the weather models. Yesterday I mentioned the possibility that the north side could get a somewhat lower snowline Saturday during the day, but the model runs suddenly presented us with a considerably more positive picture this morning. You really rarely see such differences from run to run (the evening vs the morning). The reason for the lower snowline is a more north-westerly flow during Friday, allowing significantly cooler air to flow in. One thing does remain pretty constant in the models: the westerly winds will be very strong.

What is the snowline doing? Do the models pull back?

Now the question is what impact will this have on the snowline and whether the models will pull back a bit after all? We can already see the latter happening slightly this evening, as you can see above. The cold may not reach the Western and Northern Alps to the same extent as this was calculated in the morning runs, but even so, it still looks considerably better than in recent days. Small shifts can really still happen, but here is an indication based on the current model runs:

The answer to the first question is that the snowline will likely really get lower than I wrote yesterday. For the French Northern Alps and western Switzerland in the night from Thursday to Friday depending on wind impact around 1,500 to 1,800 metres, but Friday during the day the snowline could actually drop below 1,500 metres again. Where it snows solidly and the wind is not so much present even towards 1200 metres. Further east, the snowline will also be lower.

During the night from Friday to Saturday, even colder air masses approach from the north, bringing the snowline below 1,000 metres in eastern Switzerland and Vorarlberg. West of that, it is still a bit of a question. I do not rule out that here too the snowline could get surprisingly low, but for now I am assuming around 1,200 to 1,600 metres.

As for amounts, there could still be plenty of snow, with the French Northern Alps and western Valais centred on up to around 80-120 centimetres. Some 40 - 60 centimetres of snow could also fall between Valais and Vorarlberg. Only east of Arlberg, meanwhile, the amounts are significantly less. A maximum of 10-20 centimetres, with even less likely in Salzburgerland.

Stormy!

Finally, let me emphasise: wind remains a problem! Not only for avalanches, but it also makes it harder for precipitation cooling to take place. At the western alpine edge, where the wind will be the strongest, the snowline will therefore be the highest. If you are in the Western Alps, you should look for the more inner-alpine, narrow, wind-sheltered valleys. Also, from Friday onwards, the further north, the higher the chances of a low snowline.

** Tomorrow in an update I will discuss the new model runs and where to go! **

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?