Upper Valais
Turtmanntal
Avalanche Problems
Wind slab + Persistent weak layers
2+
Field notes
Wind slab
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.
Persistent weak layers
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 are very challenging to recognise. 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 and shooting cracks are typical when present, but you can have a serious weak layer with no warning signs at the surface. Knowledge of how the Snow deposited on the ground in a multiplicity of layers.EAWS glossary has evolved is essential. SLF's travel advice is direct: travel conservatively, avoid terrain where the consequences of being caught are large, and treat the history of weather and snow as more important than what you can see today. Read the full bulletin.
Snowpack & Weather
Snowpack
Especially on shady slopes above approximately 2400 m and generally in Areas above approximately 3000 m (particularly glaciated areas).EAWS glossary, there are faceted, long-lasting 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 deep in the Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary. In many places in western and northern regions with heavy snow, these layers are overlaid with deep fresh snow and so can no longer be easily triggered by winter sports participants. However, any avalanches that are triggered in these deep layers can still become large, as has been made clear by isolated avalanches over the weekend. In regions with less snow, avalanches can more easily be triggered in deep layers of old snow and will usually be of medium size.
With southerly winds, snowdrift accumulations prone to triggering will develop on Tuesday, especially adjacent to ridgelines.
Small to medium gliding avalanches are still to be expected in the west and north.
Weather review for Monday
The night to Monday saw little but widespread snowfall. The snowfall level dropped from 1400 to 900 m. During the day, it was quite sunny in the mountains in the north and mostly cloudy on the southern flank of the Alps. Low stratus clouds lay over the Swiss plateau.
Fresh snow
From Sunday afternoon to Monday morning above approximately 1600 m:
- in the west and Lower Valais: 5 to 10 cm
- less elsewhere, dry in the south
Temperature
At midday at 2000 m, around -2°C
Wind
- Light overnight
- At times moderate to strong from southerly directions over the course of the day
Weather forecast to Tuesday
There will be low stratus cloud in the north, with only occasional sunny spells in the west due to the broken, higher altitude cloud cover. Upper Valais via Central and Eastern Switzerland to Lower Engadine will see the most sun. Conditions will be cloudy on the southern flank of the Alps and a few flakes of snow may fall above approximately 1200 m.
Fresh snow
A few flakes are possible in the south.
Temperature
At midday at 2000 m, around -1°C
Wind
- Southerly, moderate at times during the night at high altitudes, rising to strong along the Main Alpine Ridge
- Mostly light during the day
Outlook
Wednesday and Thursday will see low stratus cloud in the north, with sunny intervals above it. Conditions will be very cloudy in the south with up to 15 cm of snow falling over the two days above approximately 1200 m. Winds will be mostly light on Wednesday and mostly moderate on Thursday from southerly directions.
Avalanche risk will decrease in the north and increase slightly in the south with small amounts of fresh snow and with Snow being lifted from the snow surface and transported by wind just above the snow surface (visibility not noticeably reduced).EAWS glossary.
Avalanches, possibly large, may still be triggered in places in the Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary, especially on steep shady slopes at high altitudes. Gliding avalanches are still possible in regions with deep snow in the west and north.