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      WSL Institute for Snow and Avalanche Research SLF
               NATIONAL AVALANCHE BULLETIN NO. 93
                for Sunday, 14 February 2010
             issue date 13.2.2010, 18:30 hours
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  SITUATION IS TREACHEROUS - DANGER SUBSIDING ONLY GRADUALLY
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CURRENT CONDITIONS

On Saturday it was sunny. The midday temperature at 2000 m was 
minus 7 degrees. A light westerly to southerly wind was blowing, 
in some regions winds were at moderate velocity. 
The snow layering is unfavourable widespread, except for in the 
central part of the southern flank of the Alps. It is most 
perilous in those places where older, better consolidated 
snowdrift is deposited on top of soft, faceted layers of snow. 
With increasing altitude, the snowpack becomes somewhat better 
consolidated overall due to the sustained influence of winds.


SHORT-TERM DEVELOPMENT

On Sunday it is expected to be quite sunny, in spite of some 
cloudbanks. The midday temperature at 2000 m will be minus 8 
degrees. A light southwesterly wind will be blowing.


AVALANCHE DANGER FORECAST FOR SUNDAY

Northern flank of the Alps west of Grindelwald; eastern Lower 
Valais; Upper Valais not including upper Saastal and not 
including southern Simplon region; northern and central 
Grisons; Lower Engadine; 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 from 
Grindelwald westwards above approximately 1800 m, elsewhere 
above approximately 2000 m. In some places avalanches can be 
triggered down to more deeply embedded layers of the snowpack 
even by a single backcountry skier or freerider. The most 
treacherous spots are wherever older snowdrift accumulations 
have been deposited on top of poorly consolidated old snow. 
These places are usually covered and concealed by fresh 
fallen snow and thus, nearly impossible to recognize. 
Whumpfing sounds are warning indicators of the hazard. 
The avalanche situation is treacherous. Extensive experience 
in spotting and evaluating avalanche perils is important for 
backcountry skiers and freeriders.

Northern flank of the Alps east of Grindelwald; western Lower 
Valais; upper Saastal; southern Simplon region; Ticino; 
Upper Engadine; southern valleys of Grisons not including 
Muenstertal:
  Moderate avalanche danger (Level 2)
The avalanche prone locations are to be found on steep slopes 
in all expositions. On the northern flank of the Alps from 
Grindelwald eastwards, the danger zones are found above 
approximately 1600 m, elsewhere above approximately 2000 m. 
In isolated cases, avalanches can be triggered down to more 
deeply embedded layers of the snowpack, particularly in 
transition areas from shallow to deep snow. The lowermost 
layers of the snowpack are more stable in the central part of 
the southern flank of the Alps; there, the major danger stems 
from older snowdrift accumulations.


TREND FOR MONDAY AND TUESDAY

On Monday it will be predominantly sunny. Over the course of the 
day in southern regions, clouds will move in. On Tuesday it will 
be generally sunny in northern regions, accompanied by light 
foehn winds; temperatures will gradually rise. In southern 
regions it will be heavily overcast and a bit of snowfall down 
to lower altitudes is anticipated. The avalanche danger is not 
expected to change significantly.