Take a look at this snow map! A lot of snow is coming for the Northwest Alps. However, the colourful map fails to show one important ‘but’ and that is that the uncertainty about the snowfall (both quantities and distribution) for the weekend is still quite high. This is all related to the path of the low-pressure area. When the details become clear later this week and the signals are green, PA#1 will follow!
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Changeable on the northern side
Last night it already snowed a bit again with a cold front passage. 5 to 15 centimetres fell in the north-western Alps between Haute-Savoie and Vorarlberg. Today during the day, the cold front lies over the Eastern Alps, with similar and thus limited amounts here as well.
Tomorrow, the Azorean high tries to connect with the high over Scandinavia/Russia. It will continue to snow in the Austrian Alps (especially further east in Salzburgerland) with a slight northerly flow though. Meanwhile, the cold air is all over the place, bringing the snowline down to most valleys. Some 5 to 10 centimetres at most will still fall.
Warmer, but then soon snow again
Thursday will see temporary warmer weather from the west, but a cold front with cooler air behind it will soon follow in the night to Friday. It will take a while before this cold front moves in and the first precipitation in the north-west Alps is accompanied by a fairly high snowline. A large part of the precipitation falls in the small warm sector, so the French-Northern Alps and western Switzerland, especially the edges close to the alpine foreland, have to deal with a snowline temporarily reaching 1,800 to 2,200 metres.
As often in such situations, inner-alpine, narrow valleys have the best papers for a lower snowline. Here, cold pools in the valleys are more persistent. In the more or less isothermal structure of the atmosphere, precipitation cooling can ensure a significantly lower snowline. However, this requires strong precipitation intensity and limited wind speeds. Despite the low snowline, the snow will be fairly wet up to high elevations in these situations.
Higher up, some 15 to 20 centimetres of snow may fall in the north-west Alps, locally in the high mountains some more. Friday during the day, cooler air flows in and the snowline drops to (well) below 1500 metres during the last precipitation.
Still some uncertainties for the weekend
Until Friday, the models seem to agree pretty much. For PA#1, we look more towards the weekend, where developments are still somewhat uncertain. The position of the low pressure core that will provide the snow still varies a lot in the weather models. GFS shows the low clearly moving further north, while the European model shows a more southerly path, just north of the Alps. However, both models do show a good amount of snow for the Northwest Alps of well over half a metre. GFS only shows less and in a more limited area.
In these calculations, EC also comes up with a storm and very heavy wind gusts higher up during the weekend. GFS shows this less pronounced, as the core of the low-pressure area is further north. Needless to say, this also has a big impact on the hotspots for this upcoming PA.