At elevated altitudes a considerable avalanche danger will be encountered in some regions
Edition: 19.5.2021, 17:00 / Next update: 20.5.2021, 18:00
Snowpack
As a result of the low temperatures, any and all potential weak layers are stabilising only gradually, for which reason the fresh fallen snow and freshly generated snowdrifts of recent days still remain prone to triggering in some places at high altitudes. From place to place, avalanches can sweep along more deeply embedded layers inside the snowpack. At heightened altitudes, conditions remain wintery for this juncture of the season.
As a result of sunshine and significantly higher temperatures during the course of the day on Thursday, particularly in the regions where snowfall has been heaviest, numerous loose-snow slides and loose-snow avalanches can be expected to release from the new fallen snow.
The old snow cover is thoroughly wet below 2500 m on north-facing slopes, below approximately 3000 m on east-facing, south-facing and west-facing slopes. Wet-snow and gliding avalanches continue to be possible, particularly in case of solar radiation.
Observed weather on Wednesday, 19.05.2021
During the night on Tuesday, snowfall was registered over widespread areas in the northern regions, with the focal point on the northern flank of the Alps. During the daytime hours on the northern flank of the Alps and in northern Grisons, skies were heavily overcast accompanied by showers. In the Valais and the Engadine there were bright intervals. On the southern flank of the Alps it was predominantly sunny.
Fresh snow
The snowfall level lay between 1400 and 1800 m. Between Tuesday afternoon and Wednesday afternoon, the following amounts of fresh snow were registered above approximately 2200 m:
  • northern flank of the Alps from the Aletsch region into the Glarus Alps: 20 to 40 cm;
  • in the remaining parts of the northern flank of the Alps, in Lower Valais and in northern and central Grisons: 10 to 20 cm;
  • in the remaining regions of Switzerland, less; on the southern flank of the Alps it remained dry.
Temperature
At midday at 2000 m, between -1 °C in the northern regions and +2 °C in the southern regions.
Wind
Winds were blowing from northerly directions,
  • in the western regions predominantly at light to moderate strength;
  • in the eastern and the southern regions at heightened altitudes, predominantly at moderate strength.
Weather forecast through Thursday, 20.05.2021
In the northern regions in the morning hours, particularly on the northern flank of the Alps, there will still be residual cloud evident, and in the eastern regions the final snowflakes of this round of precipitation are expected to fall. Subsequently, it will become increasingly sunny from the west and at high altitudes. In the southern regions it will be sunny.
Fresh snow
Between Wednesday afternoon and Thursday morning, the following amounts of fresh snow are anticipated, with a snowfall level at 1200 to 1600 m:
  • northern flank of the Alps from the Aletsch region into the Alpstein, northern Prättigau, Silvretta, Samnaun: 10 to 20 cm;
  • remaining parts of the northern flank of the Alps, Valais, northern and central Grisons, Engadine: 5 to 10 cm;
  • southern flank of the Alps: it is expected to remain dry.
Temperature
Temperatures are expected to rise significantly, at midday at 2000 m to between 0 °C in the northern regions and +5 °C in the southern regions.
Wind
Winds in the southern regions, and in general at heightened altitudes, will will be blowing at moderate to strong velocity from northwesterly directions, slackening off significantly in the afternoon.
Outlook through Saturday, 22.05.2021
On Thursday night, southwesterly winds will arise and increase in intensity. On Friday morning in the foehn-exposed regions of the north, there will still be foehn-induced bright intervals evident, in the other regions of Switzerland skies will become increasingly overcast from the west and the south, accompanied by precipitation. The southwesterly winds will be blowing at strong velocity. By Saturday morning, precipitation is anticipated over widespread areas, most of which will fall in the furthermost western part of the Lower Valais: 30 to 50 cm above approximately 2400 m. On Saturday during the morning hours, showers are still to be expected, however bright intervals will be possible during the afternoon.
The danger of dry-snow avalanches continues to demand great attentiveness in high alpine regions. During the nighttime hours on Friday, avalanche danger levels in the regions where snowfall has been heaviest can increase another notch.