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      WSL Institute for Snow and Avalanche Research SLF
               NATIONAL AVALANCHE BULLETIN NO. 113
                for Tuesday, 1 March 2011
             issue date 28.2.2011, 18:30 hours
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  WIDESPREAD CONSIDERABLE AVALANCHE DANGER
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CURRENT CONDITIONS

On Monday morning, the snowfalls in the north ceased. There were bright spells over a wide area in 
the mountains during the day. In the south it was generally very cloudy. Little snow fell in 
southern Upper Valais. From Saturday evening until Monday morning, 30 to 40 cm of snow fell on 
the northern flank of the Alps, and 20 to 30 cm fell in Lower Valais. From Upper Valais through 
the Gotthard region and in northern and central Grisons and Lower Engadine, 10 to 20 cm of snow 
fell; less fell elsewhere. The midday temperature at 2000 m on Monday was about minus 5 degrees. 
The easterly wind was light to moderate.

The fresh snow of recent days, on north facing slopes in particular, is lying on faceted, soft old 
snow in some places and is prone to triggering.

SHORT-TERM DEVELOPMENT

On Monday night, approximately 10 cm of snow will fall on the main Alpine ridge in Valais. During 
the day, it will become increasingly sunny in the south. In the north it will be fairly sunny above 
the low stratus. The midday temperature at 2000 m will be about minus 1 degree. The wind will be 
light to moderate from the east.

On the northern flank of the Alps and in the high Alpine regions in particular, the easterly wind 
will be moderate at times and transport the loosely bonded fresh snow of recent days.

AVALANCHE DANGER FORECAST FOR TUESDAY

Northern flank of the Alps; Valais; Grisons excluding both Val Calanca and Val Moesa:
  Considerable avalanche danger (level 3)
  
The avalanche prone locations are steep slopes of all aspects.

They are to be found, in particular, above approximately 1600 m in the western prealps, and above 
approximately 1800 m in particular on the rest of the northern flank of the Alps excluding Urseren 
and in northern Lower Valais. The fresh snow and snow drift accumulations of recent days can be 
released easily in some places. Avalanches can reach up to medium size.

In the rest of Valais and in Urseren and Grisons, excluding both Lower Val Calanca and 
Lower Val Moesa, the avalanche prone locations are to be found, in particular, above 
approximately 2200 m. The main danger is posed by the fresh and older snow drift accumulations. 
In many cases, they are lying adjacent to the ridge line and in gullies and bowls, and in some 
cases they can be released easily.

In all regions subject to this danger level, avalanches can be triggered by a single person. Those 
engaging in backcountry touring and off-piste activities must dispose of experience in the 
assessment of avalanche danger.

Ticino; Val Calanca; Val Moesa:
  Moderate avalanche danger (level 2)
  
The avalanche prone locations are to be found, in particular, on west to north to south facing 
wind-loaded slopes above approximately 2000 m. Fresh and older snow drift accumulations are to be 
found, in particular, in areas adjacent to the ridge line and pass areas, and in gullies and bowls. 
They are generally small, but can be released easily in some cases. Careful route selection is 
important.

In view of the solar radiation, small wet snow slides are to be expected on very steep south 
facing slopes, as are loose snow avalanches in rocky areas with multiple starting zones.

TREND FOR WEDNESDAY AND THURSDAY

On each of the next two days, the weather will be mostly sunny, apart from some low stratus-like 
cloud cover. The avalanche danger will decrease slowly.