High danger of dry and wet avalanches will be encountered over a wide area
Edition: 29.12.2021, 17:00 / Next update: 30.12.2021, 18:00
Snowpack
The precipitation, which is heavy in some places, will continue into the night on Wednesday in the western regions and in the Valais, in the northern and eastern regions until Thursday. The snowfall level lies at 2500 m, in some places in the western regions even higher during the night.
As a consequence of strong to stormy westerly to northwesterly winds the new snow was intensively transported at high altitudes. On Thursday, snowdrift accumulations will continue being generated in high alpine regions more than anywhere else as a result of strong-velocity northwesterly winds. New snow and freshly generated snowdrift accumulations are prone to triggering, on west-facing, north-facing and east-facing slopes particularly so. Dry-snow avalanches can fracture to deeper down layers in the weak old snow. This applies to the regions from central Valais over the Ticino as far as Grisons more than anywhere else.
As a result of the persistent rainfall during Wednesday night, the snowpack in the western and the northern regions will become even more thoroughly wet at high altitudes. Numerous and to an increasingly extent also large-sized avalanches can be expected.
Observed weather on Wednesday, 29.12.2021
Skies were heavily overcast for the most part, accompanied by precipitation which subsequently intensified from the west starting in the early morning hours. The snowfall level ascended from the west up to approximately 2600 m by afternoon. In the northeastsern regions and the inneralpine zones the snowfall level still lay at 1200 to 1500 m. In the Sottoceneri it was partly sunny.
Fresh snow
Between Tuesday afternoon and Wednesday afternoon in the western regions above approximately 2500 m, in the eastern regions above approximately 2000 m, the following amounts of fresh snow were registered:
  • Valais not including Simplon region: 20 to 40 cm, on the French border as much as 50 cm;
  • northern flank of the Alps, Simplon region, remaining parts of Gotthard region: 20 to 30 cm;
  • northern Grisons, northern Lower Engadine: 10 to 20 cm; in the other regions of Switzerland, less or else it remained dry.
Since Monday afternoon, the following overall amounts of fresh snow have been registered:
  • Valais not including Simplon region: 40 to 60 cm, on the French border as much as 70 cm;
  • northern flank of the Alps, Simplon region, remaining parts of Gotthard region: 20 to 40 cm;
  • northern Grisons, Lower Engadine: 10 to 20 cm; in the other regions of Switzerland, only a few centimetres.
Temperature
At midday at 2000 m, between +3 °C in the western regions and -1 °C in the eastern regions.
Wind
  • In the western and northern regions, winds were westerly to northwesterly, blowing at strong to storm-strength, slackening off during the course of the day;
  • in the southeastern regions, winds were blowing predominantly at moderate strength; in the Engadine at strong velocity from northerly directions.
Weather forecast through Thursday, 30.12.2021
On Wednesday night precipitation is expected over widespread areas with the exception of the southern regions. The snowfall level will lie at 2500 m. During the daytime on Thursday, skies in the northern and eastern regions will be heavily overcast by and large and the precipitation will come to an end during the course of the day. In the western regions, skies will brighten up increasingly, in the Valais it will become increasingly sunny. In the southern regions it will be predominantly sunny. In the mountains it will be extremely mild.
Fresh snow
Between Wednesday afternoon and Thursday afternoon, the following amounts of new snow are expected above approximately 2800 m:
  • northern Alpine Ridge from the Wildstrubel as far as the Glarus Alps: 40 to 60 cm;
  • southern part of Lower Valais, remaining parts of the northern flank of the Alps and the Gotthard region, northern Grisons, northern part of Lower Engadine: 20 to 30 cm;
  • in the other regionis of Switzerland, less; south of the Main Alpine Ridge it will remain dry.
Below approximately 2400 m the entire precipitation will fall as rain.
Temperature
At midday at 2000 m, between +4 °C in the northern regions and +6 °C in the southern regions.
Wind
  • On Wednesday night on the northern flank of the Alps, winds will be westerly, blowing at moderate to strong velocity; in the southern regions winds will be northerly, blowing at moderate to strong velocity, subsequently slackening off during the daytime;
  • winds at high altitude will be northwesterly, and persist blowing at strong velocity; on the Main Alpine Ridge winds will blow at storm strength during the night.
Outlook through Saturday, 01.01.2022
Following nights of clear skies, it will be sunny and very mild in the mountains on New Year's Eve and on New Year's Day. The northwesterly winds will slacken off and be blowing predominantly at moderate strength at high altitude. The danger of dry-snow avalanches will decrease. As a result of the mild temperatures and solar radiation, wet-snow slides and wet-snow avalanches are possible on steep, rocky south-facing slopes during the course of the day. This applies particularly to the regions where recent snowfall has been heaviest.