Valais Chablais
Vouvry
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
In the west there is appreciably more snow than normal for the time of year, but significantly less in the south. In other regions, snow depths are average to slightly below average. 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 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, if avalanches are triggered in these deep layers, they can become large. In other regions, the weak old snowpack layers are closer to the surface. Here the Snow deposited on the ground in a multiplicity of layers.EAWS glossary, which is mostly still very thin, is becoming completely faceted and loose, meaning that here too avalanches can only be triggered in places.
This week's mostly small snowdrift accumulations are in some cases still prone to triggering. Gliding avalanche activity is decreasing,
Weather review for Wednesday
There were sunny intervals in the mountains in the west and conditions were quite sunny in the east. It was very cloudy on the Main Alpine Ridge and south of there.
Fresh snow
A few centimetres locally in the west and south
Temperature
At midday at 2000 m, between -1°C in the north and -3°C in the south
Wind
- Light to moderate from southerly directions, sometimes strong in regions exposed to the foehn wind in the north
- Light northeasterly in the Jura
Weather forecast to Thursday
In the north there will be low stratus cloud to around 1000 m, with quite sunny conditions above that, while the east will see sunny intervals. Conditions will be very cloudy on the southern flank of the Alps, with a little snow falling above approximately 1300 m.
Fresh snow
Main Alpine Ridge and south of there: 1 to 5 cm, in Ticino up to 10 cm
Temperature
At midday at 2000 m, around -1°C in the north and -3°C in the south
Wind
Light to moderate south to southwesterly
Outlook
Friday
In the north, it will be cloudy at first and a few centimetres of snow will fall above approximately 900 m by midday. In the afternoon, conditions will brighten up in the mountains. In the south, it will become increasingly sunny from the morning onwards. Winds will mainly be light. Avalanche danger will not change significantly.
Saturday
In the north, conditions will be mostly cloudy with light precipitation. The snowfall level will rise to between 1400 and 1700 m, with up to 10 cm of snowfall in the far west, elsewhere a few centimetres. The south will see sunny intervals with broken cloud cover. The wind will freshen, becoming moderate to strong southwesterly in the north and generally at high altitudes. Snowdrift accumulations, which are likely to be small but easily triggered, will form and avalanche danger will increase slightly.