The developments for Christmas have been very uncertain in recent days. The current high-pressure weather was extended a little, but early on it seemed that in the middle of this week things might be shaken up again. For a long time, the models seemed to show beautiful winter maps for Christmas far in advance and there was no sign of the singularity of “Weihnachtstauwetter” with mild weather during Christmas. If you have been following the models a bit since last week, you could see that the uncertainty was enormous. You often come across large differences between the model runs and models themselves. After several days in a row of great uncertainty, it now looks like it’s going to get a lot milder for the Alps around Christmas. With this transition, the chances for precipitation are also increasing.
Still a few days of calm high-pressure weather
Before things get interesting again, we will have a few more days of calm high-pressure weather in the Alps, as we have seen in the past week. Today, the tail of a cold front in the east of Austria brought some 10 centimetres of snow locally, but in the rest of the Alps it remained dry and sunny. This weather pattern will not change much until Thursday either, with the Eastern Alps sitting in a significantly colder air mass than the Western Alps.
Zonal flow
The grazing heat front with precipitation for the middle of this week had also temporarily disappeared from the maps, but is back in the European model. This situation clearly shows the uncertainty involved in this transition from high pressure to changeable weather. The high-pressure area will be pushed further and further to the southeast in the coming days, as a result of which the Alps will be situated in a more westerly flow. On Thursday, the west and north sides of the Alps in particular will experience a significant improvement. The European model predicts some precipitation in Austria later on Thursday. GFS will let this precipitation area pass north of the Alps. I expect the northern areas to have to deal temporarily with snowfall which will change into rain below 1500 meters.
Weihnachtstauwetter
A powerful depression over the Atlantic Ocean looks set to determine the weather in Central Europe from Friday onwards. The core can deepen considerably and slowly but surely moves towards the British Isles. In the night from Thursday to Friday, this will bring another portion of warm and humid air to the Alps in a gentle south-westerly flow. For the time being, this seems to bring precipitation mainly for the Western and Southern Alps and föhn conditions for the Northern Alps. The models still disagree about the amount and the distribution of the precipitation, but it doesn’t seem to be very much. So don’t take the snow chart above too literally. Maybe it’s just as well, because the snow line will temporarily reach 2000 metres or even higher in the Western Alps with this supply of mild air. The Southern Alps are a bit more favourable and it will probably stay a bit cooler. Hopefully Wednesday will bring more clarity for the weather during Christmas weekend.