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      WSL Institute for Snow and Avalanche Research SLF
               NATIONAL AVALANCHE BULLETIN NO. 86
                for Sunday, 7 February 2010
             issue date 6.2.2010, 18:30 hours
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  DANGER ZONES ARE BLANKETED OVER, CONSIDERABLE AVALANCHE DANGER 
WIDESPREAD
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CURRENT CONDITIONS

On Saturday in western and southern regions it was sunny in some 
areas, in eastern regions it was heavily overcast. The midday 
temperatures at 2000 m were minus 6 degrees in northern regions 
and minus 2 degrees in southern regions. On Friday night, the 
northerly winds were blowing at moderate to strong velocity in 
eastern and southern regions in particular; in western regions 
they were light to moderate. During the day on Saturday, the 
winds slackened off. Since Friday morning in the Lower Valais, 
on the northern flank of the Alps, in northern Grisons and in 
the central part of the southern flank of the Alps there has 
been 15 to 30 cm of snowfall, in some spots as much as 40 cm. In 
the remaining regions there was 5 to 15 cm of snowfall. 
The new fallen snow covers and conceals older danger zones, 
which makes the overall situation far more treacherous. 
Avalanches ordinarily fracture in the fresh fallen snow and 
snowdrift, yet in some places break through to the old snowpack. 
They can attain medium size. On the Main Alpine Ridge and in 
southern regions, the snow layering is more favourable, and 
breakthroughs down to the old snowpack are less probable. 
Exceedingly numerous avalanches released by backcountry skiers 
and freeriders on Saturday confirmed the highly delicate snow 
situation.


SHORT-TERM DEVELOPMENT

On Saturday night in northeastern regions, a further 5 to 10 cm 
of snowfall is anticipated. On Sunday in the Valais and in 
southern regions, it will be predominantly sunny, in northern 
and eastern regions increasingly so. The midday temperatures at 
2000 m will be minus 7 degrees in northern regions and minus 4 
in southern regions. A northeasterly wind of moderate velocity 
is expected to prevail at high altitudes in particular. 
Freshly formed snowdrift accumulations are relatively small. The 
unfavourable snow layering which is prevalent far and wide is 
not expected to improve anytime soon.


AVALANCHE DANGER FORECAST FOR SUNDAY

Northern flank of the Alps; Valais; Grisons not including Ofen 
Pass or Muenstertal:
  Considerable avalanche danger (Level 3)
The avalanche prone locations are to be found on steep slopes 
in all expositions. On the northern flank of the Alps not 
including Urseren as well as in northern Grisons, the 
avalanche prone locations are found above approximately 1600 
m; in the remaining regions of this danger level, above 
approximately 2000 m. Avalanches can be triggered by a single 
backcountry skier or freerider. In isolated cases, naturally 
triggered avalanches are also possible. New fallen snow and 
snowdrift blanket older danger zones in some places. 
Avalanches can break through to the old snowpack, 
particularly in northern regions. In the central and eastern 
parts of the Main Alpine Ridge and in southern regions, the 
major peril stems from fresh snowdrift in particular. 
Backcountry skiing and freeriding tours in outlying terrain 
away from secured ski runs require extensive experience in 
spotting and assessing avalanche hazards.

Central Ticino; Sotto Ceneri; Ofen Pass and Muenstertal:
  Moderate avalanche danger (Level 2)
The avalanche prone locations are to be found on steep slopes 
in all expositions above approximately 1600 m. Freshly formed 
as well as older snowdrift accumulations make a cautious 
route selection imperative.


TREND FOR MONDAY AND TUESDAY

On Monday it will be predominantly sunny. On Tuesday, new clouds 
will move in from the southwest and light precipitation will set 
in. The avalanche danger is expected to decrease only very 
gradually, particularly in the regions with unsound snow 
layering.