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Avalanche bulletin for Tuesday, 28 February 2017

In the west and in the south a critical avalanche situation will be encountered in some regions

Edition: 27.2., 17:00 Next update: 28.2., 18:00 Validity

In the west and in the south a critical avalanche situation will be encountered in some regions
Edition: 27.2.2017, 17:00 / Next update: 28.2.2017, 18:00
Snowpack
Weak layers exist deeper in the snowpack on shady slopes in particular at altitudes between 2200 m and 2800 m. These are most prevalent in the inneralpine regions of both Valais and Grisons. In recent days, however, avalanches have been been triggered in these deep layers only in isolated cases.
The stormy weather has transported both the fresh snow and loosely bonded old snow. Although the quantities of transportable old snow are relatively small, large snow drift accumulations have been forming in the regions exposed to heavier precipitation. As a consequence of the fresh snow and snow drift accumulations, the weak layers deeper in the snowpack are becoming more prone to triggering again in the inneralpine regions of Valais and Grisons in particular. On north and east facing slopes in particular, an increasing number of avalanches is to be expected in the weakly bonded old snow.
Observed weather on Monday, 27.2.2017
As a consequence of the strengthening southwesterly wind, the main Alpine ridge in Valais was partly cloudy, but everywhere else was quite sunny.
Fresh snow
-
Temperature
At midday at 2000 m: about +3 °C in the north and -2 °C in the south
Wind
  • The initially light to moderate southwesterly wind picked up in the afternoon
  • In the susceptible northern regions, a foehn wind developed as the day progressed
Weather forecast through Tuesday, 28.2.2017
Throughout the Swiss Alps the weather will be very cloudy and windy. Precipitation will fall, which will be heavy in the west and in the eastern part of the main Alpine ridge. The snowfall level will be approximately 1000 to 1500 m in most places, but drop to low altitudes in the southern Alpine valleys.
Fresh snow
By Tuesday evening the following amounts of snow will fall above approximately 1500 m:
  • Western Jura, Vaud and Fribourg Alps, northern and extreme west of Lower Valais, main Alpine ridge from from Val Medel to the Bernina Pass: 30 to 50 cm, and even more in some localities in the Trient region and from southern Val Bregaglia to the Piz Bernina
  • Western Bernese Oberland, rest of Lower Valais, northern Upper Valais, rest of the central part of the southern flank of the Alps: 20 to 30 cm
  • Other regions: 10 to 20 cm over a wide area, but less in the northern valleys exposed to the foehn wind
Temperature
At midday at 2000 m: about -3 °C over a wide area, and about 0 °C in the northern regions exposed to the foehn wind
Wind
  • Strong in the south, frequently storm force in the other regions, from the southwest
  • In the northern Alpine valleys, a strong foehn wind on Monday night
Outlook through Thursday, 2.3.2017
Wednesday
The persistently strong to storm force westerly wind will give rise to changeable weather with a lot of cloud and bright intervals. Snow will fall frequently and the snowfall level will drop to low altitudes. In the south there will be a strong foehn wind on Tuesday night, and it will be predominantly sunny during the day on Wednesday in central and southern Ticino in particular. The avalanche danger will increase a little over a wide area.
Thursday
On Wednesday night snow will fall in the west and north. The precipitation will cease in the morning and be followed by quite sunny weather everywhere. The westerly wind will ease a little. In the south the avalanche danger will decrease. In the other regions it will not change significantly.