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Valid until Wednesday February 29th 2012.
Main Concerns: (Avalanche problems)
Wind Slab - Wind slabs dating from the storm Friday and found on NW to E aspects may remain triggerable by humans on Monday. More recent slabs created by strong NW winds on Saturday and found on southerly aspects are more touchy to human triggers. New slabs will be formed on NW to NE aspects on Tuesday/Wednesday with new snow and wind in the coming system. These will certainly be triggerable by human loads and may even fail naturally. All of these wind slabs are a problem that will be found at tree line and in the alpine and will produce avalanches from small to large enough to bury, injure or kill a person.
Storm Slab - New snow forecast for Tuesday Wednesday may come in sufficient quantity (especially on the west coast) to make for instability in the storm snow at all elevations and on all aspects. These could produce avalanches from small to large enough to bury, injure or kill a person.
The island Alps received 60 to 80cm of snow from Friday to Sunday with the bulk of it coming on Friday. Winds were strong from the SE to SW during the precipitation and then shifted to strong from the NW on Saturday. Freezing levels were around 1300m at the start of precipitation on Friday but then dropped much lower giving low density snow from 1000m up. The outlook is as follows:
Monday: High overcast and increasing cloud during the day. No new precipitation. Light SW winds. Freezing level around 600m.
Tuesday: 20 to 30cm of snow starting later in the day. Winds increasing to moderate to strong SE. Freezing level around 500m.
Wednesday: 10 to 20cm of snow. Winds easing to light to moderate from the SE to SW. Freezing level around 500m.
60 to 80cm of new snow has been moved first by strong SE to SW winds on Friday and then by strong NW winds on Saturday to produce winds slabs at tree line and above. Surfaces in wind exposed areas vary from very stiff slabs to exposed melt freeze crust at tree line and below. The older slabs are of course less reactive now but those formed on Saturday remain somewhat reactive on Monday and new slabs which will be formed on Tuesday/Wednesday will be quite touchy to human loads. Snow surfaces on sunny aspects became moist on Sunday whereas on shady aspects small surface hoar was forming. Persistent instabilities mentioned in our previous bulletin have 'tightened up" considerably and would likely only react with a very big load in very specific terrain (alpine, shallow snow pack, shady). The lower snowpack is strong and
Natural and skier triggered avalanches to size two were observed on Friday and skier triggered avalanches to size two were observed on Saturday.
Enter the wind zone at tree line and above with caution on Monday and early Tuesday and be aware that the freshest wind slabs are on southerly aspects. Note that hazard will increase as the storm intensifies on Tuesday/Wednesday and avoid avalanche terrain in these times of loading from new snow and wind. Watch for signs of instability such as cracking and wumphing.
Prepared by Jan Neuspiel