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  INSTITUTE FOR SNOW AND AVALANCHE RESEARCH  DAVOS
               NATIONAL AVALANCHE BULLETIN NO. 26
                for Tuesday, 4 December 2007
             issue date 3.12.2007, 18:30 hours
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  WIDESPREAD CONSIDERABLE AVALANCHE DANGER WITH FRESH SNOW AND 
STRONG WIND
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CURRENT CONDITIONS

The precipitation that occurred on Sunday night was accompanied 
by stormy weather. During the day the direction of the moderate 
to strong gusty wind changed from southwesterly to 
northwesterly. Some of the precipitation was heavy, so that the 
following amounts had fallen by Monday evening: northern Lower 
Valais 40 to 60 cm; Vaud and Fribourg Alps, western Bernese 
Oberland, rest of Valais, northern Ticino and from Central 
Switzerland to the Alpstein region 20 to 40 cm; eastern Bernese 
Alps, northern and central Grisons 10 to 20 cm; Engadine 5 to 10 
cm. Further south it remained dry in most places. The midday 
temperature at 2000 m was about minus 3 degrees in the north and 
south, and about minus 4 to minus 7 degrees in the inneralpine 
regions. 
The bonding of the snowpack is favourable in many places. Some 
areas where the snowpack has been shallow thus far, however, are 
faceted and now being covered with fresh snow. The layers of 
wind-deposited snow are initially poorly bonded.


SHORT-TERM DEVELOPMENT

Further snowfalls are to be expected. By Tuesday evening a 
further 20 to 40 cm of snow will fall north of the Rhone and 
Rhine and in the Gotthard region, northern and central Grisons 
and Samnaun, but the quantity may reach as much as half a metre 
in the area from the Bernese Oberland and Central Switzerland to 
Glarus. In the remaining parts of Valais and northern Ticino, 10 
to 20 cm of snow will fall; less than 10 cm will fall in 
Engadine and the Grisons southern valleys. On Tuesday afternoon 
the precipitation will ease from west to east. The temperature 
at 2000 m will initially fall to minus 7 degrees at midday 
before rising again in the afternoon. The northwesterly wind 
will blow strong to very strong and continue to transport large 
quantities of snow.


AVALANCHE DANGER FORECAST FOR TUESDAY

Northern flank of the Alps; Valais; northern Ticino; northern 
and central Grisons; Silvretta and Samnaun:
  Considerable avalanche danger (level 3)
On the northern flank of the Alps and in Valais, northern 
Ticino, northern Grisons including Tavetsch and northern 
Surselva, as well as in Silvretta and Samnaun, the avalanche 
prone locations are to be found on steep slopes of all 
aspects above approximately 1800 m. In the remaining parts of 
central Grisons, the avalanche prone locations are to be 
found, in particular, on wind-loaded slopes of all aspects 
above approximately 2000 m. The main danger is posed by the 
fresh snow and snow drift accumulations. Experience in the 
assessment of the avalanche danger is required. Small and 
medium natural avalanches can occur, in particular, on the 
northern Alpine ridge and from Praettigau to Samnaun.

Central Ticino, the remainder of Engadine and the Grisons 
southern valleys:
  Moderate avalanche danger (level 2)
Avalanche prone locations are to be found, in particular, on 
wind-loaded slopes of all aspects above approximately 2000 m. 
Fresh snow drift accumulations are to be avoided.


TREND FOR WEDNESDAY AND THURSDAY

On Tuesday night the weather will brighten up from west to east. 
It will be quite sunny and mild during the day. Thursday will be 
changeable with some precipitation. For the time being the 
avalanche situation remains treacherous for those engaging in 
winter sports. On Thursday the avalanche danger will decrease.