We are on the eve of a very explosive weekend in the Alps. A low pressure area nestles exactly above the Alps and attracts both very cold air from the north and very warm air from the south. These air masses meet right above the Alps and it's going to be one hell of a show. If you're planning an outdoor activity in the Alps next weekend, you'd better change your plans. It will rain, as in: very intense. It will snow heavily in the high alpine where huge amounts of snow will come down. In this forecast:
The cold front I talked about earlier this week passed on Wednesday. In a much earlier forecast, the models still assumed a lot of snow for the entire Alps, but because the cold front was forced by a powerful high pressure area to follow the negative scenario, the only result was snow in Austria in the last 20 hours, especially in the east where it remained colder. The Kitzsteinhorn already got 30-40 cm of fresh snow.
Today (Thursday) the sun comes out fast. Because of the wind from the south it feels like the Föhn is going strong. It is mild, sunny and you better enjoy it, becasue there is a big storm on its way.
The weather will change from Friday. Cold polar air (the blue arrows) flows from the north to the south. This cold air can descend to the south over the eastern flank of a powerful high pressure area above the Atlantic Ocean. At the same time, in response to this, warm air flows from the south to the north in the direction of the Alps.
This battle between very cold and warm air comes to a standstill around the Alps. This can be clearly seen in the undulating movement of the red-blue line. The blue parts are the cold front that tries to penetrate to the south, the red parts the heat fronts that try to move northward. In addition, colder air shifts over warmer air one moment, but the other time warm air shifts over cold air. Both situations ensure a lot of precipitation.
With such a stationary front it is very difficult to predict where the snow line will be located exactly and it can also differ from valley to valley. Assume for the time being that the snow line in the west and north of the Alps will be between 1500 and 2000 meters, while on the south side of the Alps it will be around 2000 to 2400 meters this weekend.
The base for winter 2018-2019 might come down in the high alpine this weekend. Don't look too closely at the data that our model or other models are currently projecting. It is a highly dynamic situation that is typical for the autumn. We know where we stand after the weekend, where the snow came down and how low or how high the snow line eventually ended up.
But that it is going to be extreme is certain. Especially on the south side of the Alps, local rain quantities up to 200 mm are to be expected. Locally possible even more. In addition, a lot of snow will come down locally in the high alpine, but where exactly? We'll have to wait and see. Given the direction of the current I expect the most snow to come down from the Gotthard region via the Ortler massif up to the Wildspitze in Austria.
It will snow and it will rain on Sunday, especially in the east of the Alps after which, if the models are right, a retour d'est will follow in the night to Monday. This will bring lots of snow to the highest peaks of the Piedmont and the French Alps, later expanding to the rest of the Alps.
Stay stoked, Morris