Föhn in the Southern Alps and freezing cold in the north


By Henri on 10 February 2021 · 0

Deep winter in San Martino di Castrozza (feratel.com)
Deep winter in San Martino di Castrozza (feratel.com)

A lot will happen at the same time in the Alps on a meteorological level in the coming days. After snow will fall across the Alps today, a few changes await us. While the Western Alps are still relatively mild with some snow chances the day after tomorrow, we will have to deal with a strong Föhn in the Italian Alps tomorrow. The Eastern Alps dive into the freezer under the influence of a northeasterly current.

Snowfall today
Snowfall today

Snow from the west

Today a front with some snowfall is crossing the Alps from the west. The French Alps have already had the phase with the highest precipitation intensity. While the sun already comes out in the French Southern Alps in particular, it continues to snow lightly during the day in the French Northern Alps, so that a total of 10 to 20 centimeters can fall above 1000 meters. In the course of the morning, the snowfall spreads to the east and it will also start snowing in Switzerland and Austria. In the northwestern stau areas such as Engelberg, the snowfall can intensify again tonight, resulting in up to 30 centimeters of snow to fall here. Further east, I don't expect much more than 5 to possibly 15 centimeters.

It is also snowing heavily in Italy today. With a snow line of about 1000 to 1200 meters, all areas east of Milan can receive about 10 to 20 centimeters of snow. In the east it can snow a little longer, so that the Julian Alps again get up to half a meter of snow today. The extreme precipitation amounts shown by our weather model (up to half a meter around Trento) seem a bit unlikely to me. In the course of the afternoon, this snowfall from the west gives way to a rapidly incoming Föhn, which means that a lot less snow falls in the Piedmonte today than in the rest of the Italian Alps.

An impressive pressure gradient of no less than 16 hPa (meteocentrale.ch)
An impressive pressure gradient of no less than 16 hPa (meteocentrale.ch)

Strong northern Föhn

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The Western Alps can look forward to a beautiful day with a lot of sun tomorrow. Austria will still have to deal with some snowfall into the valleys tomorrow morning, but this will not bring a lot. During the day, the sun comes out here too. The subsidence of the high-pressure area above Scandinavia has meanwhile increased the pressure gradient above the Alps considerably. A solid Nordföhn will hit in the Italian Alps tomorrow. I don't really expect extremely high temperatures, as the upper air temperatures in the source area on the north side have also dropped sharply. Nevertheless, the maximum temperature in the valleys with a north-south orientation and the Po-valley can rise to well above 10 degrees tomorrow, locally possibly even towards 15 degrees.

The subsiding high pressure area above Scandinavia creates a northeasterly current (wetter3.de, DWD)
The subsiding high pressure area above Scandinavia creates a northeasterly current (wetter3.de, DWD)

Eastern Alps dive into the cold

While the Eastern Alps get into the arctic cold with temperatures down to -20 degrees at an altitude of 1500 meters and locally even colder on the ground in the nights, the Western Alps remain in a significantly warmer sector. This is clearly visible on the map below, which shows the temperature deviation at an altitude of 1500 meters. While Austria turns deep pink with temperatures of 12 degrees below normal, it remains relatively mild in the French Alps with values around the average or slightly above. This is because the Western Alps still have to deal with a mild westerly current, which will cause some snow on Friday.

While the Eastern Alps are in the freezer, it remains considerably warmer in the Western Alps (wxcharts.com)
While the Eastern Alps are in the freezer, it remains considerably warmer in the Western Alps (wxcharts.com)
Friday's expected snowfall is mainly limited to the Western Alps
Friday's expected snowfall is mainly limited to the Western Alps

Today, our weather model again shows considerable accumulations with quantities up to 40 centimeters, but if you compare this with the other models, our weather model is very high in these calculations. In the following days, our weather model also showed light snowfall, which is not yet reflected in the other models. I therefore assume that it will stay at about 10 to 20 centimeters on Friday. In the French Southern Alps the temperatures are still a bit high, so the snow line will fluctuate around 1500 meters. Further north it is slightly colder, so that the snow line can drop towards 1000 meters. With the exception of the west of Valais, the rest of the Northern Alps keep it dry and it will remain predominantly sunny here at least until the weekend. Only in the east of Austria there could be some snow showers with a current directly from the Baltic Sea on Sunday, but that is still very uncertain and will not cause large accumulations.

The GFS Ensemble for Innsbruck (wetterzentrale.de)
The GFS Ensemble for Innsbruck (wetterzentrale.de)

The long term

If we take a look at the ensembles, we can see a clear picture of the trend. In the Eastern Alps (puncture point Innsbruck) the upcoming precipitation moment is immediately the last noteworthy for the coming period. After the peak of the cold raid during the weekend, almost all ensemble members foresee a gradual warming with hardly any snow expected. As mentioned earlier, the Scandi high pressure descends and exerts more and more influence on the Alps. Interruptions from the Atlantic Ocean are diverted to the north just before the European continent. After the snow this weekend, it also seems to be getting drier in the Western Alps. The ECWMF is going along with this for the time being, but will show precipitation from the west again in the middle of next week.

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