We are heading for some turbulent days in the Northwestern Alps. On Sunday, I already talked about the developments for this week. A huge amount of snow is going to fall higher up, but at the same time it will be stormy and warm. This means the snowline will be very high. Rain will be inevitable. In Austria, the inflow of colder air on Saturday may allow snow with a lower snowline.
In this weather report
Before the rain is coming, the western Alps will get around 5 to 10 centimetres of fresh snow later in the afternoon and evening after a sunny start to the day. Thereby, especially in the northern areas, the snowline will still be quite low. Here, I expect a snowline of around 1,000 metres. Also Wednesday morning, some snow will still fall with a similar snowline, possibly already several hundred metres higher. During the day, it will remain changeable, but milder air will be brought in and the snowline will shoot up.
For a while last week, it seemed that the border of two air masses with vastly different temperatures, could temporarily touch the north side of the Alps. At this air mass boundary, a lot of snow can fall and the northern Alps seemed to benefit for a while. Unfortunately, those calculations disappeared at a rapid pace and the air mass boundary was calculated further north bit by bit. Tomorrow is the day and the boundary is now calculated over central Germany, far away from the Alps. The Alps are in the warm sector.
What does this deliver? The snowline will rise on Wednesday during the day due to the supply of mild air. The sheltered inner-alpine areas may see a fairly low snowline for longer, but winds also increase, limiting the effects of precipitation cooling. It will snow very hard and a clap of thunder is also possible. Until Thursday morning, snow amounts are already decent. I still expect around 30 to 40 centimetres of snow, locally maybe even half a metre. With the rising snowline, the snow will be quite heavy though, even above the tree line.
The wind will also be a real problem. Wednesday especially in the morning along the French northern Alps and then also in Switzerland and western Austria. Especially at the northern alpine edge, wind speeds of 100 to 120 kilometres per hour could occur. After that, the winds temporarily decrease slightly, but remain strong. A new strong wind field will follow on Wednesday evening. The powder falling in the high mountains will thus be accompanied by stormy winds and thus also serious wind slabs.
On Thursday, calm returns temporarily. In the morning in the French Northern Alps, some residual snow will remain, after which it is mainly the Alps northern edge that will still have to reckon with some showers (with snow above 1500-1800 metres). In the Western Alps it may temporarily clear up a bit. Important here is not to underestimate the avalanche danger. The fresh pack of snow higher up may be very tempting, but combined with strong winds it will be very tricky. So avoid steep terrain and check the local avalanche bulletins thoroughly when heading out.
A new precipitation area is approaching the Western Alps during the night from Thursday to Friday. Temporarily (inner Alps possibly a little longer too) with a snowline of around 1,500 metres, but by evening at the latest another portion of mild air will flow in. Then follows the real heavy precipitation with once again stormy winds (not only higher up, but also down into the valleys), lots of precipitation and a snowline that could reach around 2100-2300 metres according to current calculations. So, with amounts of widespread 100mm precipitation, it will be bad for the lower areas. They will really struggle. Higher up, of course, there will be loads and loads of snow, but conditions will be far from ideal. Too low and you are in the rain, but higher up it will be very tricky with a whiteout, the large amounts of snow, stormy winds, closed lifts and a very high avalanche risk.
Further east, large amounts could also fall. Up to and including Vorarlberg, well over 50mm of precipitation could fall with a snowline also lingering around 1800-2000 metres, although Saturday's snowline here could possibly drop a bit during the day, see below. The areas beyond such as Tyrol and the Salzburgerland are slightly more in the precipitation shadow with the exception of the northern areas. Here, however, there is a bit more chance that the snowline could drop considerably during Saturday due to the inflow of cooler air from the northwest, but this is not yet a certainty. Of course, I will keep an eye on this in the coming days. More on this in a next update!