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      WSL Institute for Snow and Avalanche Research SLF
               NATIONAL AVALANCHE BULLETIN NO. 83
                for Sunday, 30 January 2011
             issue date 29.1.2011, 18:30 hours
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  CAUTION URGED TOWARDS FRESHLY FORMED SNOWDRIFT ACCUMULATIONS
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CURRENT CONDITIONS

On Saturday it was overcast on the southern flank of the Alps, in the remaining regions it was 
partially cloudy, coming from the south. The midday temperatures at 2000 m were between 
minus 4 degrees in northwestern regions and minus 8 degrees in southern regions. The southerly wind 
was blowing lightly, although wind velocity was intermittently moderate on the northern Alpine Ridge 
and in Grisons in particular.

As a result of the southerly wind, further snowdrift accumulations have formed which can be easily 
triggered from place to place. More deeply embedded inside the snowpack, there are also hard packed 
layers which are directly adjacent to softer layers of faceted crystals and grains. These soft 
layers are thickest in the inneralpine regions. In general, however, the old snowpack evidences 
little tendency towards fracture propagation.


SHORT-TERM DEVELOPMENT

In general on Sunday, it will be heavily overcast on the southern flank of the Alps, in the 
remaining regions predominantly sunny. The midday temperatures at 2000 m will be minus 3 degrees. 
The wind will be blowing at light to moderate velocity, initially coming from southerly directions, 
then shifting to easterly over the course of the day.


AVALANCHE DANGER FORECAST FOR SUNDAY

Northern Alpine Ridge from Chablais to the Susten region not including northern Valais; central and 
eastern parts of the northern flank of the Alps; Gotthard region; central Grisons not including 
Main Alpine Ridge; in addition, the regions Flims-Untervaz, Schanfigg, Davos, Silvretta:
  Moderate avalanche danger (Level 2)
  
In the indicated regions of the northern flank of the Alps not including the Gotthard region, the 
avalanche prone locations are located primarily on wind loaded slopes of western to northern to 
eastern exposition above approximately 2000 m.

In the Gotthard region, in central Grisons not including the Main Alpine Ridge, in addition in the 
regions of Flims-Untervaz, Schanfigg, Davos and Silvretta, the avalanche prone locations are to be 
found primarily on steep slopes of western to northern to eastern exposition above approximately 
2400 m.

In all regions of this danger level, freshly formed snowdrift accumulations have been deposited in 
areas adjacent to ridge lines, in pass areas and in gullies and bowls more than anywhere else. They 
can from place to place be easily triggered, however remain small sized and are quite visible as a 
rule.

Furthermore, particularly in the indicated regions of Grisons, more deeply embedded layers inside the 
snowpack can be triggered especially through large additional loading. Very steep places with 
shallow snow in particular, such as transition areas into gullies and bowls, should be evaluated 
with great care.

Western part of the northern flank of the Alps north of the northern Alpine Ridge; Valais not 
including the regions of Chablais and Obergoms; Ticino not including the Gotthard region; remaining 
parts of northern and central Grisons and of the Engadine; southern valleys of Grisons:
  Low avalanche danger (Level 1)
  
Isolated avalanche prone locations are to be found primarily in shady, extremely steep terrain at 
high altitudes. Avalanches are expected to fracture down to the old snowpack only seldom; this 
applies particularly to the inneralpine regions of the Valais. Freshly formed snowdrift 
accumulations should be avoided particularly in extreme terrain. The danger of being swept along 
and falling should be taken into consideration.


TREND FOR MONDAY AND TUESDAY

In all regions of the Swiss Alps, it is expected to be predominantly sunny. Temperatures will rise 
somewhat in the mountains. The avalanche danger is expected to change only insignificantly.