A strong high pressure area in northern Europe turns the wind to the east over the course of this week. Colder, continental air is brought in, so we generally expect little snow. Nevertheless, some snow does seem possible, especially for (some regions) in the southern Alps. Before that happens, we take a look at today's and tomorrow's expected snow.
In this weather report:
Unfortunately, last weekend it became clear again that we are still dealing with pre-season conditions. On the Pitztaler Glacier a snowboarder went off-piste next to the Wildspitzbahn yesterday. He slipped and ended up in a glacier crevasse. Fortunately, people going up in the Wildspitzbahn saw the accident happen and mountain rescue was soon on hand. Read here the full article (in German).
The thin snow cover not only creates a problem at glacier crevasses, but the avalanche risk is significant in much of the Alps, especially on steep north-facing slopes. A skier can easily hit a weak layer due to the thin snow cover and thus trigger an avalanche. SLF reports, for example (on 25.11, an update follows today at 5pm):
Lower Valais, central Valais, northern Alpine Ridge, northern Grisons and northern Lower Engadine Avalanche prone locations for dry-snow slab avalanches are to be found particularly on shady slopes, in the western regions above approximately 2200 m, in the other regions of Switzerland above approximately 2400 m. Weak layers in the old snow are now blanketed over by layers of fresh snow and freshly generated snowdrifts, making the avalanche prone locations difficult to recognize. Medium-sized avalanches can be triggered even by one single person; and in the western and the northern Lower Valais large-sized avalanches can be triggered in isolated cases. A defensive route selection is called for.
At the time of writing, a front with snowfall is approaching from the west. In the French Alps, it could bring around 5 to 10 centimetres of snow. The further west, the more snow I expect. The westernmost areas could possibly get up to 20 centimetres of snow until tomorrow afternoon, the areas closer to the alpine main ridge significantly less. In the French Northern Alps, the snowline will drop to (well) below 1,500 metres, in the French Southern Alps it will be slightly warmer and the snowline will remain several hundred metres higher.
We then see the front stalling over the Alps. The strengthened high pressure area over Eastern Europe weakens the elongated front and prevents it from moving eastward. Tomorrow, the front is even pushed back slightly westwards. Between central Switzerland, Salzburgerland and the Dolomites, some 5 to 15 centimetres of snow could also start falling as a result during the night and tomorrow during the day. Most models calculate the largest snowfall accumulations over the Bregenzerwald, Allgäu and Arlberg. Here, locally, even up to 20 centimetres of snow might fall. The snowline may drop to just below 1,000 metres in most places. With temporarily strong precipitation, it may even snow down into the valleys due to precipitation cooling.
Looking higher up in the atmosphere, we see a bubble of cold air of this weak trough moving south towards the Mediterranean, where the low-pressure area over the warm water surface may strengthen. Initially, this seems to bring snow only for Greece and the Balkans, but it is possible that this low-pressure area will still provide a surprise in the Alps later this week.
The rest of the week will be mainly cloudy for the northern and eastern Alps. On the western side it clears up more and more from Wednesday onwards. Over the Alps, we see an increasing easterly wind component under the influence of the strong high pressure area in northeastern Europe. This continental air is colder, but at the same time drier. It will not yet be bitterly cold as we sometimes see with easterly winds, because due to the location of the high-pressure area, the flow will occasionally come from the southeast instead of the (north)east. This offers chances for some snow in the Alps after all.
Small shifts could still have a big impact on the expected snowfall in the southern Alps. In recent days, for instance, we saw some maps come through with retour d'Est signals. It is indeed true that high pressure northeast of the Alps is favourable for a retour d'Est to develop, but that does not mean that everything is certain yet. For now, it looks like the Southeast Alps (Slovenia, Carinthia, Dolomites) will get some snow (10 to 20 centimetres) from the second half of the week with a south-easterly flow. Some more snow may follow from the weekend, but the models still differ too much on this.
For the German speakers among us: White Risk SLF will give an AvaLounge presentation tonight at 7pm in which, among other things, they will explain the new method of splitting avalanche risk 3 into 3-/3+. You can watch the presentation via this livestream on Youtube: