Lots of snow again today, warmer during the weekend

Yesterday, Chris discussed the snowfall in detail. In the past 48 hours, it has snowed a lot higher up. All in all, these are serious amounts that will become the base for the season. At the L’Ecreuleuse measuring station (Les Marécottes), for instance, 120 centimetres have already fallen at 2252 metres altitude. Surrounding measuring stations at similar altitudes show 50 to 80 centimetres on a large scale. The values are so variable due to strong winds. The snowfall map below gives a good estimate of the distribution for Switzerland.

Last night, with a northwesterly flow some more snow fell, especially in Switzerland, with a snowline all the way down into the valleys. The result is a deep-winter setting as seen above from Attelas (2727m) in Verbier.

Last days’ snowfall was accompanied by heavy wind gusts. Around the alpine main ridge (especially on the Italian side), the föhn flow added to it. In the areas that are already open in this part of the Alps (e.g. Zermatt and Saas-Fee), do not underestimate this risk of slabs.

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New low brings more snow

Today, a new low pressure area from the west will once again bring a lot of snow during the day. A strong jet stream aiming right at the northwest Alps sent the low pressure system in this direction. The core could also deepen considerably in the last 24 hours in the process (20-25 hPa within 24 hours). Over France, we therefore see a strong wind field. The snowfall, which reaches the Alps later today, is accompanied by heavy wind gusts.

Another point of attention will be the snowline for the Western Alps. This is because it is not equally low everywhere. The front map clearly shows that the warm sector (between the warm front and the cold front) reaches the French Alps and western Switzerland. This translates into the supply of warm air at all altitudes (see our temperature map at 1500m altitude above).

First of all, it starts snowing to most valleys, but as the warm air moves in, the snowline rises considerably for a while. In the western French areas on the Alpine fringe, it may temporarily rain up to 2000m. In western Switzerland and the rest of the French Alps, the snowline rises to around 1600-1800 metres in most places. The further east, the longer the snowline stays relatively low.

During the night into Friday, cold air is brought in again at the back of the low-pressure area and the snowline drops rapidly. Most of the snow will have fallen by then, though.

Up to half a metre of snow

The snowforecast shows well where the hotspots of this snowfall are. Most is expected in the Northwest Alps from Haute-Savoie to the Glarus Alps. Here, 30 to 50 centimetres of snow will fall, locally higher up some more. We do not encounter these largest amounts until above 2000 metres due to the high snowline. Large parts of Austria and Italy are on the leeward side of this precipitation, keeping the amounts here very limited.

So on Friday, the Alps are back in the cold air, with a northwesterly flow bringing some snow on the northwest side during the day. Clearing skies are possible especially in the inner Alps in the morning and in the eastern and southern Alps. The nordföhn will provide considerable wind there.

At the northern Alpine edge, snow showers will be more frequent. During the night into Saturday, the focus of these showers shifts more to the Austrian side. Before Saturday during the day the high pressure area takes over, some 5 to 15 centimetres of snow could fall here.

Warmer over the weekend

The cold air masses are only short-lived, as significantly warmer air follows from the southwest on Saturday. In the map of upper-air temperature anomalies (850hPa ~ 1500 metres), the “warm pizza slice” with anomalies of +6 to +12 degrees compared to the climatological average is clearly visible. A strong low pressure area has formed to the west of Britain, which will more or less stay in place over the weekend and pump warm air from West Africa towards central Europe.

Throughout the Alps, this will make it significantly milder. The strong south-westerly flow will create a föhn setting on the northern side, which will make it even warmer here. Temperatures in the föhn valleys will rise to around 15 degrees and it will also be mild at altitude. Snow covers at lower altitudes will therefore struggle. Higher up in the north-west Alps, by then, enough has fallen for a good base, but the föhn can create some extra wind slabs.

The weakened cold front of the low-pressure system approaches on Monday evening, according to current calculations. On Tuesday during the day, the front also moves further towards the eastern Alps. It does not seem to get much colder in the process. The snowline will probably end up at values around 1,500 metres. In the north-west Alps, the front may deliver 10 to 20 centimetres, but in the eastern Alps I don’t expect much more than 5 centimetres. In the Dolomites, it may stay completely dry.

Developments after that are still uncertain. The GFS calculates a high-pressure ridge with little chance of precipitation for the Alps, but the European model shows more changeable weather with small layers and a cold upper air. We’ll keep an eye on it!