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  INSTITUTE FOR SNOW AND AVALANCHE RESEARCH  DAVOS
               NATIONAL AVALANCHE BULLETIN NO. 162
                for Friday, 18 April 2008
             issue date 17.4.2008, 18:30 hours
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  SNOWDRIFT IN NORTHERN REGIONS, SNOWFALL IN SOUTHERN REGIONS
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CURRENT CONDITIONS

On Thursday it was quite sunny in northern regions. In southern 
regions it was overcast and a few centimeters of snow fell above 
approximately 1500 m. The midday temperatures at 2000 m were 
minus 1 degree in northern regions, minus 3 degrees in southern 
regions. Moderate southerly winds prevailed. In the regions 
typically subject to foehn influence, winds were at times strong 
and transported the snow, particularly in areas adjacent to 
ridge lines and above 3000 m. Through the daytime warming curve, 
natural wet avalanches were loosed, some of which fractured all 
the way down to the ground.


SHORT-TERM DEVELOPMENT

On Friday there will be foehn influence in northeastern regions, 
with sunny spells especially during the afternoon. In western 
and southern regions it will be predominantly overcast. In the 
central part of the southern flank of the Alps above 
approximately 2000 m, 20 to 40 cm of new snow is expected by 
Friday evening. On the remaining Main Alpine Ridge there will be 
10 to 20 cm, further northwards 5 to 10 cm. Midday temperatures 
at 2000 m will be plus 2 degrees in northern regions and minus 1 
degree in southern regions. Moderate southerly winds will 
continue to prevail and are expected to transport the snow, 
particularly in higher altitude areas adjacent to ridge lines.


AVALANCHE DANGER FORECAST FOR FRIDAY

Guttannen; Gadmer Valley; central part of the northern flank of 
the Alps not including Prealps; in addition, Linthal; 
Sernftal; southern Simplon region and central part of the 
southern flank of the Alps:
  Considerable avalanche danger (Level 3)
In the central part of the southern flank of the Alps and in 
the southern Simplon region, the avalanche prone locations 
are to be found on steep slopes in all aspects above 
approximately 2200 m. The danger level is mainly contingent 
on the amounts of new snow. To begin with at least, natural 
avalanches are improbable. 
In the indicated regions on the northern flank of the Alps, 
the avalanche prone locations are to be found in west to 
north to east facing areas adjacent to ridge lines above 
approximately 2500 m in particular. The freshly formed 
snowdrift can easily be triggered.

Remaining northern flank of the Alps; remaining Valais; 
remaining Grisons:
  Moderate avalanche danger (Level 2)
The avalanche prone locations are to be found on southwest to 
north to southeast facing steep slopes. In the remaining 
Valais, the avalanche prone locations are found above 
approximately 2200 m, on the remaining northern flank of the 
Alps and in the remaining Grisons above approximately 2000 m. 
Recently formed snowdrift accumulations should be assessed 
with great care. Above 3000 m, the hazards are 
correspondingly higher.

In all regions, caution must be exercised towards the dangers of 
wet avalanches. In southern regions at medium altitudes, wet 
avalanches are possible at any and all times, due to the rain. 
In northern regions, wet avalanches can be expected primarily 
due to solar radiation and the daytime warming curve. This is 
particularly the case on steep, sun-flooded slopes below about 
2500 m.


TREND FOR SATURDAY AND SUNDAY

On Saturday, more snowfall is expected in southern regions. In 
northern regions the foehn-dominated sphere of influence will 
continue. On Sunday it will be predominantly sunny. The 
avalanche hazards will continue to increase in southern regions. 
However, the danger is unlikely to reach the level "high".