The weather is going to become quite varied after Friday with temperatures due to rise as an active warm front moves into the Alpine region from the west bringing precipitation for the northwest of the Alps.
Over the next few days the rain/snow limit will fluctuate very much and could reach as high as 2400m for some time in the northern French and north-western Swiss Alps where there will be a significant loss of snow depth and snow quality below 1800m. High-altitude ski resorts in the north-western Alps like Tignes, Verbier, Engelberg and the Jungfrau will see significant snow on the upper section of their ski areas.
To begin with, on Friday the storm brings rain and snow to the northern French, Swiss and eventually western Austrian Alps later in the day and overnight. Most of the snowfall will occur between Friday noon and Saturday 00h. The rain/snow limit ascends to 2200m or even higher in some (north-)western parts of the Alps, such as Chamonix, the Portes du Soleil and the Trois Vallees.
Heavy rainfall, in a relatively short period of time, accompanied with snow melt at lower-to-mid altitude may cause flooding in the western Alps.
In turn, cold air will flow into the north of the Alps during the course of the Saturday. At the same time precipitation moves to the north of the Alps and the snow line then drops towards 1900m. Dry powder-ish snow is most likely to fall above 2100m. On the southern side of the Alps, including the French Southern Alps a northern Föhn will dominate resulting in predominantly sunny weather.
On Sunday afternoon, once again, mild air flows into the northern Alps. The cold air of Saturday afternoon is forced out by a southwestern current. The mild and humid air of Sunday afternoon resides just north of the Alps and is trapped between the cold air that descends from the north to the Alps on the one hand and the Alps on the other. That cold air presses that damp air against the Alps and the result is snowfall deeper in the valleys in the night to Christmas.
On Monday cold air reaches the northern Alps. It descends over the eastern flank of a high-pressure area towards the Alps.
The northern Alps are most likely to get some cold air during the Christmas period, the low mountain ranges of the western Alps (French Alps, west of Switzerland and northwestern Italy) remain mainly under the spell of mild air. Because the northern Alps benefit more from the cold fronts, there is still some snow coming down on the lower parts of the mountain on our way to Christmas.
Generally speaking, the further south you are over the next few days, the lighter and patchier any precipitation will be, with some areas (such as the Dolomites) likely to stay completely dry.
The low altitude ski resorts of the northern and western Alps are going to suffer substantially over the next days. For the very best snow conditions you need to aim high, where there will be fresh snow, or south, which will avoid most of the rain.
As a consequence of the rain more frequent small and, in isolated cases, medium-sized wet and gliding avalanches are to be expected below approximately 2200m.
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