Changeable weather is back, but rain will be inevitable


By Henri on 23 December 2021 · 0

The "Weihnachtstauwetter" will strike again this year, unfortunately. A zonal flow will bring quite mild air to the Alps in the coming days. Rain, especially for the Western Alps, seems unavoidable. After a temporary cooling in the middle of next week, the weather models now show strong signs of very warm weather in the Alps during the New Year.

Warm front passes just north of the Alps (wetter3.de, DWD)
Warm front passes just north of the Alps (wetter3.de, DWD)

Warm front

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Today, after another freezing night, it will be dry and fairly sunny for a large part of the Alpine arc. Locally, low clouds may still cause it to remain grey in the valleys. The first signs of a passing warm front will become visible in the Northern Alps during the day in the form of increasing cloud cover. Tonight, some light precipitation may fall as a result of the passage of this warm front. Because the valleys are still filled with cold air and the upper air is already warming up, the northern side of the Alps might locally have to deal with black ice! The precipitation will not be much and will not completely penetrate into the inner Alpine areas. Also tomorrow and Saturday the northern areas of the Northern Alps might get some precipitation. During Christmas Eve, a strong and moist south-westerly flow in the French Southern Alps may bring a lot of precipitation. For most ski resorts, it won't be much more than 10 centimetres and the snowline will be around 2000 metres.

Fight between warm and cold air masses above Central-Europe (wxcharts.com)
Fight between warm and cold air masses above Central-Europe (wxcharts.com)
Fairly warm (south)westerlies in the Alps (wetter3.de, DWD)
Fairly warm (south)westerlies in the Alps (wetter3.de, DWD)

The weather in the coming days will be determined by a strong depression over the Atlantic. The depression itself will not bring a lot of precipitation, but it will bring rather mild air masses from the west. You'll see that on Friday the cold will flow from the north to the Alps, but the strong western flow will prevent this so the Alps will stay on the mild side.

Saturday (Christmas Day) it will remain dry in most parts of the Alps, but heavily cloudy. Only the northern areas of the Northern and Southeastern Alps seem to get some precipitation, but most of it will fall south of the Alps, including in the Northern Apennines. With the high temperatures and strong winds, the snowline will be around 2000 metres for a long time, which is at an altitude of the highest peaks in this region. During the night from Saturday to Sunday, the French Northern Alps and Switzerland will receive some more precipitation with a snowline around 1700 metres, but this will not bring more than 5 to 10 centimetres in the higher areas either. Our snow forecast map shows a lot of snow for Boxing Day, but the new model calculations hardly show any precipitation for both the Northwest Alps and the Southern Alps.

Precipitation for the western Alps after Christmas (wetter3.de, DWD)
Precipitation for the western Alps after Christmas (wetter3.de, DWD)

Precipitation from the west, then temporarily colder

After Christmas, a low-pressure area will approach from the west, which can bring a lot of snow to the Western and Southern Alps from Monday onwards. In the Southern Alps there will be colder air presen than in the Western Alps. It's likely that the Western Alps will have to deal with a lot of rain up to a possible 2000 meters altitude because of the strong winds and mild temperatures. In the higher areas, there's still a chance of a lot of snow, but the avalanche risk will also increase with this snowfall due to the stormy winds.

The models still disagree on how the low pressure area will move forward (GFS predicts a north-eastern direction over the English Channel, ECMWF more to the east), but the Northern Alps will probably receive some snow with slightly lower temperatures. In any case, it will still be too warm for snow down into the valleys.

Temperature anomaly at an altitude of 1500 metres (wxcharts.com)
Temperature anomaly at an altitude of 1500 metres (wxcharts.com)
GFS Ensemble for Geneva (wetterzentrale.de)
GFS Ensemble for Geneva (wetterzentrale.de)

Significant warming around New Year's Eve

Towards the end of the year, a very mild south-westerly flow will bring significantly high temperatures to the Alps. Both the ECMWF and GFS now show temperatures up to 15 degrees in the lowest valleys, but also higher up it will be very mild with deviations up to over 12 degrees warmer than the climatological average. In the GFS ensemble for Geneva above, we first see the gradual cooling down until a few days after Christmas and then the big temperature jump around New Year's Eve.


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