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      WSL Institute for Snow and Avalanche Research SLF
               NATIONAL AVALANCHE BULLETIN NO. 106
                for Saturday, 27 February 2010
             issue date 26.2.2010, 18:30 hours
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  CRITICAL AVALANCHE SITUATION WIDESPREAD IN OUTLYING TERRAIN 
AWAY FROM SECURED SKI RUNS
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CURRENT CONDITIONS

On Friday it was heavily overcast in most regions and in western 
and northern regions there was snowfall. Between Thursday and 
Friday afternoon above approximately 2200 m there were the 
following amounts of snowfall: Lower Valais, Vaud and Fribourg 
Alps as well as the western Bernese Alps, 20 to 40 cm; in the 
furthermost western regions, as much as 50 cm; eastern Bernese 
Alps, central part of the northern flank of the Alps, Upper 
Valais, Ticino and Grisons, 10 to 20 cm; eastern part of the 
northern flank of the Alps, maximum 10 cm. The midday 
temperatures at 2000 m were between minus 4 degrees in northern 
regions and minus 2 degrees in southern regions. The very gusty 
winds, from westerly directions, were moderate to strong in 
northern and western regions, and of light to moderate velocity 
in eastern and southern regions. 
Above all else in western regions, fresh snowdrift accumulations 
have formed which are quite deep in places. In addition, 
embedded well inside the snowpack are loosely packed layers of 
old snow which are prone to triggering, particularly below 2400 
to 2700 m and in terrain with a shallow snowpack. At 
intermediate altitudes the snowpack has been made thoroughly wet 
by the rainfall, especially so in the western regions.


SHORT-TERM DEVELOPMENT

On Saturday it will be predominantly sunny to begin with, 
accompanied by high altitude clouds. Over the course of the day, 
dense cloudbanks will move in from the west and towards evening 
precipitation is expected to set in. The midday temperature at 
2000 m will be minus 1 degree. During the night, the wind will 
shift to northwesterly and prevail intermittently at storm 
strength. On Saturday, the wind will shift to southwesterly and 
slacken off to moderate, although in high alpine regions it will 
remain strong. 
Through the solar radiation and the daytime warming cycle, the 
likelihood of avalanches triggering will increase somewhat over 
the course of the day.


AVALANCHE DANGER FORECAST FOR SATURDAY

Northern flank of the Alps; Valais; northern Ticino; Grisons:
  Considerable avalanche danger (Level 3)
In the Vaud and Fribourg Alps, in the western Bernese 
Oberland, in western Lower Valais and in northern Valais not 
including Goms, the avalanche prone locations are to be found 
on steep slopes in all expositions above approximately 
1800 m. Avalanches can easily be triggered and attain medium 
size. In isolated cases, naturally triggered avalanches are 
possible. 
On the remaining northern flank of the Alps, in northern 
Ticino as well as in Val Calanca and in Val Moesa, the 
avalanche prone locations are to be found primarily on wind 
loaded slopes in all expositions above approximately 1800 m. 
In the remaining Valais and in Grisons not including Val 
Calanca and not including Val Moesa, the avalanche prone 
locations are to be found on steep slopes in all expositions 
above approximately 2000 m. 
In all regions of this danger level, avalanches can easily be 
triggered by a single backcountry skier or freerider. 
Particularly in the inneralpine regions of the Valais and 
Grisons, avalanches can also fracture in the deeper layers of 
the old snowpack. Extensive experience in spotting and 
evaluating avalanche hazards, together with great restraint, 
are necessary in outlying terrain away from secured ski runs.

Central Ticino; Sotto Ceneri:
  Moderate avalanche danger (Level 2)
The avalanche prone locations are to be found on steep slopes 
in all expositions above approximately 1800 m. Freshly formed 
snowdrift accumulations can be easily triggered in some 
areas. They should be avoided whenever possible. A cautious 
route selection is imperative.

In all regions, below about 2000 m, particularly on very steep 
hillsides and grass covered slopes, wet snow avalanches and full 
depth snowslides are possible. They can attain medium size in 
some areas.


TREND FOR SUNDAY AND MONDAY

On Sunday in western and southern regions above 2000 m, some 
snowfall is anticipated. In eastern regions there will be bright 
intervals accompanied by foehn wind. The southerly wind will be 
strong to stormy. On Monday it will be variably cloudy. The 
avalanche danger may increase somewhat in southern regions on 
Sunday and is expected to subside on Monday.