Valais Chablais
Vouvry
Day Risk Profile
Avalanche Problems
Wind slab + Persistent weak layers
3-
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
In southern Valais, Ticino and the inneralpine regions of Grisons, there are distinct 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 deposited on the ground in a multiplicity of layers.EAWS glossary. At the weekend, human activity triggered lots of medium and sometimes large avalanches in the weak Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary in these regions, often from a distance.
Snow deposited on the ground in a multiplicity of layers.EAWS glossary structure is somewhat more favourable on the northern flank of the Alps and in northern Valais, but there are 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 deeper in the snowpack in these regions too. These may still be triggered, especially where there is little snow and at transitions from a deep to shallow snowpack.
During the night to Tuesday, snow will fall on this weak Snow deposited on the ground in a multiplicity of layers.EAWS glossary in the south and naturally triggered avalanches are possible. Snowdrift accumulations will form in many areas with the strong to stormy southwesterly winds. In many places, these will be deposited on an unfavourable surface of Snow grains, solid, with multiple flat glassy faces and sharp edges. Developed from faceting metamorphism, usually poorly bonded to one another (fewer contact points), a critical factor in avalanches if a faceted layer is covered with bonded snow. Typical grain size: 0.5 to 3 mm See also: www.snowcrystals.itEAWS glossary or Transparent, frequently flat crystals forming on the snowpack when moist air settles on the surface. It forms most often during cold, clear, humid nights. Once it is blanketed by fresh fallen snow, surface hoar is one of the most critical weak layer. See also: www.snowcrystals.itEAWS glossary. This means that the fresh snowdrift accumulations will often be easily triggerable.
Weather review for Monday
It was mostly sunny in the north and very cloudy in the south.
Fresh snow
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Temperature
At midday at 2000 m, between 0 °C in the north and -6 °C in the south
Wind
- Increasingly moderate to strong southwesterly winds
- A moderate to strong foehn wind blew in the Alpine valleys of the north.
Weather forecast to Tuesday
Snow will fall down to low altitudes on the Main Alpine Ridge and south of there. Otherwise, it will be partly sunny with some precipitation at times.
Fresh snow
From Monday evening to Tuesday afternoon:
- Main Alpine Ridge from the Lukmanier Pass to the Bernina Pass: 15 to 25 cm
- Central part of the southern flank of the Alps: 10 to 20 cm
- rest of the Main Alpine Ridge: 5 to 15 cm; elsewhere: less or dry.
Temperature
At midday at 2000 m, between -2 °C in the north and -5 °C in the south
Wind
- Strong to stormy southwesterly wind during the night, strong to stormy foehn wind in the Alpine valleys of the north
- Subsiding somewhat during the day
Outlook to Thursday
On Wednesday it will often be cloudy and a little snow will fall in the south. On Thursday it will be quite sunny in the north, but only partly sunny in the south. There will be a light to moderate southerly wind on both days.
The avalanche danger will decrease somewhat in all regions. However, it will decrease only very slowly in southern Valais, Ticino and Grisons due to the distinct and 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.