As a consequence of new snow and wind a considerable avalanche danger will be encountered over a wide area
Edition: 16.5.2021, 17:00 / Next update: 17.5.2021, 18:00
Snowpack
As a result of strong-velocity westerly winds in some places, the fresh snow and also near-surface, loosely packed old snow was transported over the weekend. Snowdrift accumulations were generated which were prone to triggering. As a consequence of westerly winds and fresh snowfall, the snowdrift accumulations continued to gather. The snowdrift accumulations of this last week are still prone to triggering in the high alpine regions more than anywhere else. At elevated altitudes, conditions are still wintery for this juncture of the season.
The old snow cover on north-facing slopes below 2500 m, on east-facing, south-facing and west-facing slopes below approximately 3000 m, is thoroughly wet. Wet-snow and gliding avalanches continue to be possible, particularly in case there is solar radiation.
Observed weather on Sunday, 16.05.2021
Nighttime skies on Saturday night were overcast, and there was precipitation over widespread areas, most of which fell in the western and the northern regions. During the daytime hours on Sunday, skies in western and northern regions were predominantly overcast, the precipitation was shower-like. The snowfall level lay between 1600 and 2000 m. In the furthermost southern regions and in the east, it was sunny to some extent during the morning hours; in the afternoon, skies were overcast, accompanied by showers from place to place.
Fresh snow
Between Saturday afternoon and Sunday afternoon, the following amounts of snow were registered above approximately 2400 m:
  • furthermost western part of Lower Valais, northern Alpine Ridge from Les Diablerets into the Glarus Alps, Alpstein region: 10 to 20 cm; in the furthermost western regions on the French border as much as 30 cm;
  • elsewhere in the northern regions, 5 to 10 cm over widespread areas; it remained dry for the most part in the furthermost southern regions, in central Grisons and in Upper Engadine.
Temperature
At midday at 2000 m, +1 °C in the northern regions, +4 °C in the inneralpine and the southern regions.
Wind
  • Winds in the western and northern regions were blowing at moderate to strong velocity from westerly directions;
  • in the other regions of Switzerland, winds were predominantly light to moderate, blowing from westerly to southwesterly directions.
Weather forecast through Monday, 17.05.2021
On Sunday night, skies will be heavily overcast for the most part and precipitation is anticipated over widespread areas, some of which will be thunderstorms. The snowfall level is expected to descend from 2000 m down to approximately 1400 m during the night. In the southern regions, only a small amount of precipitation is anticipated in the early part of the night, subsequently skies will clear up in the latter part of the night.
During the daytime in the western regions, skies will be heavily overcast, accompanied by precipitation. In the other regions of the north, skies will be variably cloudy, accompanied by sunny intervals as well as showers and thunderstorms. The snowfall level will lie at 1600 m. On the southern flank of the Alps it will be quite sunny as a result of northerly winds, accompanied by convective cloud build-up during the course of the day.
Fresh snow
Between Sunday afternoon and Monday afternoon, the following amounts of fresh snow are anticipated above approximately 2200 m:
  • northern and furthermost western parts of Lower Valais: 30 to 40 cm;
  • remaining parts of the northern Alpine Ridge and remaining parts of Valais not including southern Simplon region, as well as northern Grisons, northern Lower Engadine: 10 to 20 cm; on the northern Alpine Ridge as much as 30 cm from place to place;
  • in the remaining regions of Switzerland, 5 to 15 cm over widespread areas; only a few centimetres in the furthermost southern regions.
Temperature
At midday at 2000 m, between -1 °C in the northern regions and +3 °C in the southern regions.
Wind
  • Winds in the western and northern regions will be blowing at strong velocity, intermittently at storm strength, from westerly directions;
  • elsewhere in Switzerland at moderate to strong velocity in high alpine regions from westerly directions;
  • in the Ticino, a moderate northerly foehn wind will arise.
Outlook through Wednesday, 19.05.2021
In the northern regions, skies will be variably cloudy accompanied by precipitation and intermittent sunny intervals. The snowfall level will lie at 1400 m to 1600 m. On the southern flank of the Alps it is expected to be quite sunny, accompanied by convective cloud build-up and showers from place to place during the course of the day. The westerly-to-northwesterly winds will still be blowing at strong velocity on Tuesday, subsequently will slacken off on Wednesday.
The danger of dry-snow avalanches is not expected to change significantly on Tuesday. On Wednesday the danger levels will incrementally decrease. In the major areas of precipitation, moist-snow avalanches can be expected to trigger from the fresh fallen snow in case of solar radiation. In the southern regions the danger of wet-snow avalanches is expected to increase somewhat during the course of each day.