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  INSTITUTE FOR SNOW AND AVALANCHE RESEARCH  DAVOS
               NATIONAL AVALANCHE BULLETIN NO. 160
                for Wednesday, 16 April 2008
             issue date 15.4.2008, 18:30 hours
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  TREACHEROUS AVALANCHE SITUATION IN SOME REGIONS AFTER SNOWFALL
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CURRENT CONDITIONS


On Tuesday it was overcast in the north. A frontal system arose 
on the northern flank of the Alps. In the south it was generally 
sunny. In the west there were some bright spells in the 
afternoon. Since Sunday evening, the following amounts of snow 
have fallen: Gotthard region, Urn Alps, Central Switzerland and 
Glarus Alps 40 to 60 cm; rest of the northern flank of the Alps, 
northern Valais, rest of Ticino and northern Grisons 20 to 40 
cm; southern Valais, central Grisons, Engadine and Grisons 
southern valleys 10 to 20 cm. Midday temperatures at 2000 m were 
about minus 5 degrees in the north and minus 3 degrees in the 
south. The wind was light to moderate from the northwest. 
The fresh snow is mostly quite loosely packed. At high altitude 
it was transported moderately. The bonding with the old snowpack 
remains unfavourable for the time being in some places, 
especially where the snow fell on a crust.


SHORT-TERM DEVELOPMENT

The snowfall in the northeast will cease on Wednesday. By 
Wednesday midday a further 5 to 15 cm of snow will fall on the 
northern flank of the Central and Eastern Swiss Alps and in 
northern Grisons. Bright spells will occur in the afternoon. In 
the west and south it will be rather pleasant at first, but 
cloud will build up there in the afternoon. Midday temperatures 
will be about minus 5 degree in the north and minus 3 degrees in 
the south. The westerly wind will be light to moderate, but also 
strong at high altitudes. Fresh snow drift accumulations will 
form at high altitudes in particular.


AVALANCHE DANGER FORECAST FOR WEDNESDAY

High regions of the Bernese Alps from Wildstrubel to Grimsel; 
Gadmertal; northern flank of the Central and Eastern Swiss 
Alps; Gotthard region; northern and central Grisons; 
Engadine; Muenstertal:
  Considerable avalanche danger (level 3)
The avalanche danger is greatest in the Gotthard region and 
the Urn and Glarus Alps. The avalanche prone locations are to 
be found on steep slopes of all aspects above approximately 
2000 m. Those engaging in backcountry touring and off-piste 
activities must dispose of extensive experience and exercise 
caution. Isolated, medium-sized natural avalanches are 
possible. 
On the remainder of the northern flank of the Alps and in 
northern Grisons, the avalanche prone locations are to be 
found in particular on wind-loaded slopes of all aspects 
above approximately 2200 m. Careful route selection is 
important. 
In the rest of central Grisons and in Engadine and 
Muenstertal, the avalanche prone locations are to be found in 
particular on west to north to east facing steep slopes above 
approximately 2400 m. Avalanches can penetrate the weakly 
bonded old snow cover.

Rest of the northern flank of the Western Swiss Alps; rest of 
Valais, rest of Ticino; Val Calanca; Val Moesa; Bergell and 
Puschlav:
  Moderate avalanche danger (level 2)
The avalanche prone locations are to be found on steep slopes 
of all aspects above approximately 2200 m. The main danger is 
posed by the fresh snow drift accumulations. Careful route 
selection is important. At high altitudes, the avalanche 
danger is a little greater.

In all regions, in particular below approximately 2400 m, the 
sun and warming during the day will give to the expectation of 
loose snow avalanches and wet snow slides.


TREND FOR THURSDAY AND FRIDAY

In the west and south it will be cloudy and a little snow will 
fall at times. In the northeast the foehn wind will give rise to 
bright spells. The danger of dry avalanches will decrease. The 
danger of wet snow avalanches will increase during the day.