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      WSL Institute for Snow and Avalanche Research SLF
               NATIONAL AVALANCHE BULLETIN NO. 51
                for Sunday, 3 January 2010
             issue date 2.1.2010, 18:30 hours
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  CONSIDERABLE AVALANCHE DANGER IN SOME REGIONS
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CURRENT CONDITIONS

On Saturday in northern regions, it was heavily overcast in general. In southern regions it was 
predominantly sunny, accompanied by northerly foehn winds. Between Friday midday and Saturday 
afternoon on the northern flank of the Alps from the eastern part of the Bernese Oberland into 
the Alpstein region there was 20 to 40 cm of snowfall, locally as much as 60 cm. In the remaining 
western parts of the northern flank of the Alps, in Urseren, in Lower Valais, in northern and 
central Grisons as well as in the northern Upper Engadine there was 10 to 20 cm of snowfall, 
elsewhere less. The midday temperatures at 2000 m were minus 14 degrees in northern regions and 
minus 11 degrees in southern regions. Gusty northwesterly to northerly winds of moderate strength 
were blowing.

The new fallen snow is extremely loosely packed. At high altitudes, snowdrift accumulations have 
formed which are prone to triggering. In the Valais and the inneralpine regions of Grisons in 
particular, the base of the snowpack at high altitudes is weak in places.

SHORT-TERM DEVELOPMENT

On Sunday in the northern regions it will be partly sunny amidst high altitude cloudbanks. In the 
southern regions it will be predominantly sunny. The midday temperatures at 2000 m will be minus 10 
degrees in western regions and minus 12 degrees in eastern regions. The westerly to northwesterly 
wind is expected to slacken off Saturday night and subsequently prevail at light to moderate 
strength.


AVALANCHE DANGER FORECAST FOR SUNDAY

Northern flank of the Alps not including Prealps; in addition, Valais; northern Ticino; Grisons not 
including the regions of the Lower Engadine, Puschlav and Muenstertal:

  Considerable avalanche danger (Level 3)

On the northern flank of the Alps excluding the Prealps and Urseren and in the northern Lower Valais, 
the avalanche prone locations are to be found on steep slopes in all expositions above approximately 
1800 m. The major hazards stem from the most recent new fallen snow and fresh snowdrift masses. 
Avalanches can in some places sweep along the older layers of snowdrift which formed in the final 
days of 2009. Even a single person can trigger slab avalanches. Naturally triggered avalanches are 
possible in isolated cases, particularly in the central and eastern parts of the northern flank of 
the Alps.

In the remaining parts of the Valais, in Urseren, in northern Ticino and in the indicated regions of 
Grisons, the avalanche prone locations are to be found primarily in wind loaded slopes in all 
expositions above approximately 2200 m. Freshly formed snowdrift accumulations can easily be 
released. In addition, particularly in transition areas from shallow to deep snow, avalanches can 
be triggered in the old snowpack. Naturally triggered avalanches are possible in isolated cases, 
primarily on the Main Alpine Ridge. In all regions of this danger level, extensive experience in 
reading and assessing the avalanche situation is imperative for all backcountry skiing and freeriding 
tours.

Northern Prealps; Lower Engadine; Puschlav; Muenstertal; central Ticino; Sotto Ceneri:

  Moderate avalanche danger (Level 2)

The avalanche prone locations are to be found on steep slopes in all expositions. In the northern 
Prealps as well as in central Ticino and Sotto Ceneri, the avalanche prone locations are to be found 
above approximately 1600 m; in the Lower Engadine, above approximately 2000 m. In all regions of this 
danger level, however above all in central Ticino and Sotto Ceneri, freshly formed snowdrift 
accumulations must be evaluated with great care. In the Prealps, the major peril lies in the new 
fallen snow; in the Lower Engadine and in the Puschlav and the Muenstertal, slab avalanches can even 
be triggered in more deeply embedded layers of the old snowpack. A cautious route selection is 
essential.

TREND FOR MONDAY AND TUESDAY

It is expected to be generally overcast. In northern and western regions, a bit of snowfall is 
anticipated. The avalanche danger will recede only gradually.