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Avalanche bulletin through Friday, 30 June 2017

Avalanche danger in high alpine regions

Edition: 28.6., 17:00 Next update: In the event of heavy snowfall Validity

Avalanche danger in high alpine regions
Edition: 28.6.2017, 17:00 / Next update: In the event of heavy snowfall
Avalanche danger
Avalanche danger is limited to high alpine regions by and large.
On Thursday, as a result of fresh fallen snow above approximately 3500 m and winds which in some places were blowing at strong velocity, critical conditions prevail widespread on the northern flank of the Alps from the eastern Bernese Oberland into the Glarner Alps as well as on the Main Alpine Ridge from Monte Rosa into the Bernina region. The fresh fallen and freshly drifted snow can easily be triggered. Isolated naturally triggered avalanches can also be expected. For backcountry tours in high alpine regions, conditions are unfavourable. In the remaining regions of Switzerland as well as below approximately 3500 m, cautious assessment of the freshly formed snowdrift accumulations in particular is called for. Even a sluff or small slide can force a fall in extremely steep terrain.
On Friday, no further naturally triggered dry-snow avalanches are expected. Backcountry tours in high alpine regions continue to require experience in assessing avalanche dangers on-site. Moist-snowslides can be expected to release from the new fallen snow.
Snow and weather
Snowpack
Prior to the precipitation there was a cohesive, area-wide snowpack on north-facing slopes in high alpine regions as well as in glaciated regions. The old snow was thoroughly wet and well settled. The uppermost surfaces of the snowpack were highly irregular, thus making the receptive surfaces more favourable as regards the snowfall.
Weather review to Tuesday, 27 June
On Monday night there was a small amount of precipitation. Following a quiet interim during the daytime on Tuesday, precipitation set in again from the southwest as evening approached. On Wednesday skies were for the most part heavily overcast, excluding some bright intervals in western regions, accompanied by showerlike precipitation. In southern regions there was heavy rainfall. The snowfall level on Tuesday was at approximately 3300 m, on Wednesday it dropped down to nearly 3000 m. Above approximately 3500 m, the following amounts of fresh fallen snow were registered:
  • Main Alpine Ridge from Monte Rosa into the Bernina region: 50 to 70 cm;
  • northern flank of the Alps from the eastern Bernese Oberland into the Glarner Alps, remaining parts of Grisons: 30 to 50 cm;
  • western sector of the northern flank of the Alps, remaining parts of Valais: 10 to 30 cm.
The wind on Wednesday was blowing generally at light to moderate strength, intermittently at strong velocity, from southerly directions.
Weather forecast through Friday, 30 June
In the mountains on Thursday, skies will be heavily overcast accompanied by precipitation. This will come to an end on Thursday night. During the daytime on Friday skies will be variably cloudy. In eastern and southern regions, showerlike precipitation will recommence during the afternoon. On Wednesday night in northern regions, the snowfall level is expected to descend down to nearly 2400 m, in southern regions to approximately 2800 m. On Friday the snowfall level on both sides of the Alps will be approximately 200 m lower down. Between Wednesday evening and Friday evening above approximately 3000 m, the following amounts of fresh fallen snow are anticipated:
  • northern flank of the Alps from the eastern Bernese Oberland as far as Liechtenstein, Grisons, Ticino: 30 to 60 cm;
  • remaining regions of Switzerland: 10 to 30 cm.
On both days, winds will be blowing from westerly directions at moderate to strong velocity.
Outlook
On Saturday skies are expected to be heavily overcast by and large and a small amount of precipitation is expected in northern regions in particular. On Sunday in northern regions, showerlike precipitation is anticipated, in southern regions it will become increasingly sunny, accompanied by northerly winds. The snowfall level in northern regions will be at approximately 2500 m. The danger of dry-snow avalanches continues to require special caution in high alpine regions. As daytime warmth and solar radiation increase, moist sluffs can be expected to release from the fresh fallen snow in southern regions in particular.

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