Considerable avalanche danger will be encountered over a wide area
Edition: 17.5.2021, 17:00 / Next update: 18.5.2021, 18:00
Snowpack
A sometimes strong southwesterly to northwesterly wind has transported the fresh snow and loosely bonded old snow near the surface in recent days. Snow drift accumulations have formed, some of which are deep. Fresh snow and snow drift accumulations are prone to triggering at elevated altitudes. In some places, avalanches can release deeper layers of the snowpack. At elevated altitudes, conditions are more wintry than usual at this time of year.
The old snowpack is thoroughly moist below 2500 m on north facing slopes, and up to approximately 3000 m on east, south and west facing slopes. Both wet snow and gliding avalanches remain possible, in particular under the influence of solar radiation.
Observed weather on Monday, 17.05.2021
Sunday night was mostly very cloudy, except in the far south. Precipitation fell over a wide area, most heavily in the west. The snowfall level dropped during the night to approximately 1400 m. During the day it was mostly very cloudy in the west, but there was variable cloud with showers and sunny spells in the north. The snowfall level was approximately 1600 m. On the southern flank of the Alps it was quite sunny with a northerly wind, but convective cloud built up during the day.
Fresh snow
From Sunday afternoon until Monday afternoon, 20 to 40 cm of snow fell in Lower Valais, and 10 to 20 cm fell in the rest of Valais and on the rest of the northern Alpine ridge, as well as in some regions of northern Grisons and in Lower Engadine. Given the showery nature of the precipitation, local differences in the amounts were substantial in some cases. From Saturday afternoon until Monday afternoon, the following aggregate amounts of snow fell above approximately 2400 m:
  • Lower Valais, regions of Upper Valais from Lötschental via Leuk into Turtmanntal: 40 to 60 cm, but locally up to 70 cm
  • Rest of the northern Alpine ridge from the Vaud Alps to the Titlis: 20 to 30 cm, but locally up to 40 cm
  • Elsewhere: 10 to 20 cm, but locally up to 30 cm
  • Southern flank of the Alps excluding the southern Simplon region, and in central Grisons and Upper Engadine: a few centimetres or none
Temperature
At midday at 2000 m: about -1 °C in the north and about +3 °C in the south
Wind
From westerly directions
  • On Sunday night in the west and north, moderate to strong, otherwise light to moderate
  • During the day on the northern flank of the Alps and in the high Alpine regions, moderate to strong, otherwise light to moderate
In Ticino, light to moderate north foehn
Weather forecast through Tuesday, 18.05.2021
Monday night will be frequently cloudy with light precipitation. South of the main Alpine ridge, the night will be clear. During the day in the north, there will be variable cloud with showers and occasional sunny spells. The snowfall level will be approximately 1500 m. The south will be fairly sunny, but convective cloud will build up in the afternoon.
Fresh snow
From Monday afternoon until Tuesday afternoon above approximately 2000 m:
  • Lower Valais, northern Alpine ridge: 5 to 10 cm, but locally up to 20 cm
  • Elsewhere: a few centimetres, but none on the southern flank of the Alps
Temperature
At midday at 2000 m: between 0 °C in the north and +4 °C in the south
Wind
Moderate to strong from the west to northwest, easing during the day
Outlook through Thursday, 20.05.2021
Wednesday
In the north there will be variable cloud with precipitation and occasional sunny spells. The snowfall level will be approximately 1300 m to 1500 m. On the southern flank of the Alps it will be quite sunny with convective cloud and local showers as the day progresses.
The danger of dry avalanches will not change significantly. In the regions with precipitation, moist snow avalanches are likely to be released in the fresh snow in case of exposure to solar radiation. On each of the coming days in the south, the danger of wet snow avalanches will increase as the day progresses.
Thursday
Wednesday night will be predominantly clear on the southern flank of the Alps. Otherwise, a little further precipitation will fall over a wide area; above approximately 1400 m it will fall as snow. During the day it will be mostly sunny in the west and south. The east will become increasingly sunny once the residual cloud disperses in the morning.
The danger of dry avalanches will decrease slowly. The danger of wet snow avalanches will vary during the day.