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      WSL Institute for Snow and Avalanche Research SLF
               NATIONAL AVALANCHE BULLETIN NO. 125
                for Sunday, 13 March 2011
             issue date 12.3.2011, 18:30 hours
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  CAUTION URGED TOWARDS FRESH SNOWDRIFT
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CURRENT CONDITIONS

During the morning hours of Saturday in northern regions there were still bright intervals. Then in 
the afternoon, clouds swept in rapidly. In southern regions it was overcast, subsequently light 
precipitation set in. The midday temperatures at 2000 m were between plus 4 degrees in the foehn 
exposed regions of the north and minus 3 degrees on the southern flank of the Alps. The southerly 
wind was blowing at moderate strength on the southern flank of the Alps, elsewhere it was strong. 
Over the course of the day, increasing amounts of snow were transported, particularly in the foehn 
influenced regions on the northern flank of the Alps. The freshly formed snowdrift accumulations 
can be easily triggered, but generally are small sized.

SHORT-TERM DEVELOPMENT

On Sunday, the southerly foehn winds will intensify. On the Main Alpine Ridge from the Monte Rosa 
region into the Bernina region and southwards therefrom, 20 to 40 cm of snowfall is anticipated. 
The snowfall level will be at 1000 m. In the regions bordering on the north and on the remaining 
Main Alpine Ridge, 10 to 20 cm of new fallen snow is expected. Further to the north, hardly any 
snowfall is anticipated. The southerly wind will be blowing at moderate to strong velocity on the 
southern flank of the Alps and will transport the fresh fallen snow in particular. In the remaining 
regions, the foehn wind will blow at strong to storm velocity and transport even the old snow. The 
freshly formed snowdrift accumulations can be easily triggered and are expected to grow in size and 
frequency over the course of the day.

AVALANCHE DANGER FORECAST FOR SUNDAY

Entire region of the Swiss Alps:
  Considerable avalanche danger (Level 3)
  
The avalanche prone locations on the Main Alpine Ridge from Saastal to the Bernina Pass and 
southwards therefrom are to be found primarily on steep slopes of southwestern to northern to 
southeastern exposition above approximately 1800 m. On the northern flank of the Alps not including 
the Gotthard region, in the remaining Valais and in remaining Grisons, the avalanche prone locations 
are to be found primarily on wind loaded slopes of western to northern to eastern exposition. In the 
indicated regions of the northern flank of the Alps, the hazardous zones are above approximately 
1600 m, in the indicated regions of the Valais and Grisons, the danger zones are above approximately 
2200 m.

In all regions of the Swiss Alps, the major peril stems from freshly formed snowdrift accumulations. 
In the major areas of precipitation in southern regions, these hazardous zones are more widespread 
than in the remaining regions. The snowdrift accumulations are poorly bonded with the old snowpack 
and can be easily triggered even by a single backcountry skier or freerider. A prudent route 
selection is important.

Below approximately 2500 m, moist sluffs and, in isolated cases, wet snow avalanches are possible, 
particularly in the foehn influenced regions.


TREND FOR MONDAY AND TUESDAY

On Monday, the precipitation will taper off in southern regions. On Tuesday afternoon in southern 
regions, a new phase of precipitation will set in. In northern regions, it is expected to be quite 
sunny on both days. The wind will slacken off significantly. The avalanche danger will recede.