It will be a crazy last week of the year for the western and northern Alps. We will have to deal with heavy rainfall and a very high snowline. Up to 100 millimetres of precipitation could fall in the French Northern Alps and all the way to the Arlberg. The rain will deal a serious blow to the snow cover below 1,800 metres and may also cause local flooding and wet-snow avalanches.
Today the first precipitation front will reach the Western Alps. This front will bring some cold, so the snowline will not be too high yet, around 1500 to 1800 metres. I don't expect more than 10 centimetres of snow with this first snowfall, but just after midnight, the second wave of precipitation will arrive. This warm front will also bring the first portion of warm air. From the French Northern Alps to Central Switzerland, there might be 30 centimetres of snow, locally even up to half a metre, but only above 2200 metres.
During the night from Tuesday to Wednesday, the precipitation will intensify and the entire north-western Alps will be in the line of fire. The high-pressure area over the Iberian Peninsula will also allow even more warm air masses to reach the Alps. The wind picks up even more and the snowline rises to well over 2500 metres. On the west side, it could temporarily rain up to 3000 metres. Bizarre conditions for the end of December. With amounts of 50 millimetres or even more on Wednesday the conditions will be harsh. On Thursday, it clears up from the west, but it will continue to rain in Austria. The snowline here is also well above 2000 metres, in the northern areas even around 2500 metres.
So, where to go in the next few days? The West and North Alps will be no fun. If you are too low, you are skiing in the pouring rain and if you go higher, the stormy winds will throw a spanner in the works. Most of the lifts will not be able to run due to the wind and avalanche danger. So there is basically one good option left where it's all a bit calmer: the Southern Alps. It will be warm here too, but with the exception of the areas close to the Alpine main ridge, it will remain dry.
Lots of snow in the Western Alps. Due to the moisture input of the rain, the snow cover will become considerably heavier. Wet snow avalanches will become an increasing problem this week. The high temperatures in combination with the rain and the snowmelt up to high altitudes will also increase the risk of flooding.
After the rain, the anti-winter weather is not over yet. Around New Year's Eve, the Alps and all of Central Europe will be experiencing a winter heatwave. Especially at altitude the temperatures will rise significantly (up to 16 degrees warmer than normal at 1500 metres), but also in many valleys the temperature will rise to values that would not be out of place in spring.
Cooling down for the Alps will most likely follow right after the weekend, in the Northwest Alps possibly with a nice layer of snow, but there are also signs that we'll have another warm phase after that. An arctic outbreak with long-lasting cold and lots of fresh snow is unfortunately not in the weather charts at the moment.