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      WSL Institute for Snow and Avalanche Research SLF
               NATIONAL AVALANCHE BULLETIN NO. 69
                for Sunday, 16 January 2011
             issue date 15.1.2011, 18:30 hours
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  MODERATE AVALANCHE DANGER IN WIDESPREAD AREAS
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CURRENT CONDITIONS

On Friday night in the central and eastern parts of the northern flank of the Alps and in northern 
Grisons, there was a few centimeters of snowfall. During the day on Saturday, it was predominantly 
sunny in the mountains. In the Prealps and in the valleys, residual clouds lingered in some places. 
The midday temperatures at 2000 m were between minus 1 degree in northeastern regions and plus 5 
degrees in western regions. The northwesterly wind was blowing intermittently at strong velocity on 
Friday night, during the day on Saturday winds were of moderate strength.

The snowpack is moist up to high altitudes. In the northern regions it is thoroughly wet below 
approximately 2000 m. At high altitudes, fresh, generally small sized snowdrift accumulations have 
formed. In the central parts of the Valais and Grisons, the snowpack in widespread areas contains 
layers of old snow embedded inside it which consist of loosely packed, faceted crystals.


SHORT-TERM DEVELOPMENT

On Saturday night, the skies will be predominantly clear with quite adequate outgoing long wave 
radiation. During the day on Sunday, it will be sunny. The midday temperature at 2000 m will be 
very mild, at plus 7 degrees. The southwesterly wind will be blowing at light strength. The mild 
temperatures will bring about a consolidation of the uppermost surface layers of the snowpack, 
particularly on very steep, south facing slopes. On north facing slopes at higher altitudes, the 
snow will remain cold.


AVALANCHE DANGER FORECAST FOR SUNDAY

Swiss Alps not including the Prealps and not including Sotto Ceneri:
  Moderate avalanche danger (Level 2)
The avalanche prone locations are to be found above approximately 2200 m. On the northern flank of 
the Alps not including the Prealps, in the Valais and in Grisons not including the regions 
Val Calanca and Val Moesa, the hazardous zones are to be found on steep slopes in all expositions. 
In the central part of the southern flank of the Alps not including Sotto Ceneri, the avalanche 
prone locations are to be found particularly on steep slopes of western to northern to southeastern 
exposition as well as in areas adjacent to ridge lines in all expositions. Apart from the relatively 
small sized, freshly formed snowdrift accumulations, avalanches can be triggered primarily through 
large additional loading. The likelihood of avalanches being triggered tends to increase with 
ascending altitude on the northern flank of the Alps, in northern Grisons and in the Lower Engadine 
in particular.

In southern Valais and in central Grisons more than anywhere else, avalanches which are triggered in 
more deeply embedded layers of the faceted old snowpack are also possible in isolated cases. Such 
avalanches will most probably occur in places with shallow snow, such as in transition areas into 
gullies and bowls. A prudent route selection is imperative.

Prealps; Sotto Ceneri:
  Low avalanche danger (Level 1)
  
In the Prealps, dry avalanches are no longer to be expected, due to the thoroughly wet snowpack. In 
Sotto Ceneri, the avalanche prone locations are to be found primarily on extremely steep, shady 
slopes.

Below approximately 2400 m in all regions of the Swiss Alps, particularly on very steep south facing 
slopes, isolated wet snow avalanches and full depth snowslides can be expected over the course of 
the day. Below glide cracks, skiers and freeriders should not linger any longer than necessary.


TREND FOR MONDAY AND TUESDAY

On Monday it is expected to be predominantly sunny. On Tuesday it will be partly overcast in northern 
regions, sunny in southern regions. The temperatures are expected to drop slightly. The hazards of 
dry avalanches will gradually subside. The danger of wet snow avalanches will be somewhat subject to 
a daytime warming cycle.