Central Prealps
Stoos
Day Risk Profile
Avalanche Problems
Wind slab
2=
Field notes
Look for fresh snow deposits on Slope facing downwind/ wind sheltered aspect. Snow deposits can attain several times average snow depth.EAWS glossary, in Usually a steep, elongated, eroded trench; typically prone to snowdrift accumulation.EAWS glossary and Rounded or elongated concavity; typically tending to accumulate snowdrift.EAWS glossary, and behind ridgelines and abrupt changes in terrain — these are where the wind has loaded the snow into slabs that are easy to trigger. Recent avalanches, shooting cracks under your weight, and Distinctive noise (resembling a “whumpf” sound) occurring when a weak layer beneath a slab collapses. The air of the weak layer is forced outside the snowpack, with the resulting whumpf sound being heard. The sound usually indicates an unstable situation and can be accompanied by surface cracking. A whumpf is a clear avalanche alert.EAWS glossary sounds are clear confirmations of the problem. The safest move is to avoid wind-loaded terrain entirely. NB wind signs alone don't always mean an avalanche problem exists, and the age of drifted snow is hard to judge.
Snowpack & Weather
Snowpack
In the regions south of a line from the Rhône to the Rhine, the persistent Snowpack layer in which the crystals are poorly bonded and the layer has the potential to fail. Typical crystals in dry weak layers causing avalanches are : precipitation particles; surface hoar; faceted crystals; hollow crystals; graupel. Generally >1mm in size, loose grains with few bonds Wet weak layers can be formed by all snow crystal/grain types.EAWS glossary that have persisted since the beginning of January are still present. The number of places where human activity can trigger avalanches in the weak layers of the Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary has now decreased significantly. However, any avalanches may still become large.
In the regions north of a line from the Rhône to the Rhine and in the extreme west of Lower Valais, the Snowpack layer in which the crystals are poorly bonded and the layer has the potential to fail. Typical crystals in dry weak layers causing avalanches are : precipitation particles; surface hoar; faceted crystals; hollow crystals; graupel. Generally >1mm in size, loose grains with few bonds Wet weak layers can be formed by all snow crystal/grain types.EAWS glossary in the Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary are thickly covered and triggering by human activity is therefore unlikely. The danger here is primarily due to drifted new snow.
With temperatures falling, further moistening of the Snow deposited on the ground in a multiplicity of layers.EAWS glossary and deeper Snowpack layer in which the crystals are poorly bonded and the layer has the potential to fail. Typical crystals in dry weak layers causing avalanches are : precipitation particles; surface hoar; faceted crystals; hollow crystals; graupel. Generally >1mm in size, loose grains with few bonds Wet weak layers can be formed by all snow crystal/grain types.EAWS glossary has slowed down. Gliding avalanche activity has also decreased significantly over the last few days.
Weather review for Thursday
Overnight to Thursday, some snow fell above approximately 1400 m. Over the course of the day, conditions gradually became sunny in the west and south, but the northern flank of the Alps and northern Grisons saw only sunny intervals.
Fresh snow
From Wednesday evening to Thursday morning, above 1600 m:
- extreme west of Lower Valais and northern Lower Valais, northern flank of the Alps: 10 to 20 cm
- Jura, rest of Valais and northern Grisons: 5 to 10 cm
- less elsewhere
Temperature
At midday at 2000 m, between -1 °C in the north and +2 °C in the south
Wind
- During the night in the north initially moderate to strong from westerly directions, then easing and veering to the north
- Light during the day
Weather forecast to Friday
Skies will mostly be clear overnight to Friday. During the day, conditions will mostly be sunny in the north, with sunny intervals in the south.
Fresh snow
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Temperature
At midday at 2000 m, between +2 °C in the north and -1 °C in the south
Wind
- Mostly light overnight
- During the day in the north, increasingly moderate to strong from the southwest
Outlook to Sunday
In the south, there will be precipitation, which will be heavy from Saturday morning to Sunday morning. In the north, precipitation will move in from the west on Saturday, while there will be broken cloud with isolated showers on Sunday. The snowfall level will drop from 1500 m to around 1200 m in the south and to low altitudes in the north. A total of 60 to 80 cm of snow will fall on the main Alpine ridge from Monte Rosa to the San Bernardino Pass and south of there, while around 100 cm will fall in western Ticino. Around 50 cm of fresh snow will fall on the rest of the main Alpine ridge between the Great St. Bernard and Bernina Pass and on the central part of the northern flank of the Alps, with less falling elsewhere. There will be moderate to strong winds from southerly directions on Saturday which will then ease.
The wind and fresh snow mean that the danger of dry avalanches will increase in many areas, significantly so on the central part of the main Alpine ridge and south of there, where increasing numbers of naturally triggered avalanches are to be expected. The danger level may rise to 4 (high) overnight to Sunday, while in western Ticino an increase to level 4 (high) is probable.