Valais Chablais
Monthey-Val d'Illiez
Avalanche Problems
Wind slab + Persistent weak layers
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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.
Wet snow
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Field notes
Rolling snowballs, deep penetration when you step or ski, and small natural slides are clear signals that the Snow deposited on the ground in a multiplicity of layers.EAWS glossary is losing strength. After a clear, cold night the surface often freezes into a strong supporting Layer of hard-compacted snow resulting from a melt-freeze process or wind.EAWS glossary, and conditions are favourable in the early morning. After a warm, overcast night, the problem may be present from the start of the day. Plan early returns and watch the runout zones below you.
Snowpack & Weather
Snowpack
Sunday’s fresh and drifted snow has bonded well with the existing snow surface. Especially in the regions exposed to the most precipitation in southern Grisons, avalanches may in places still be triggered in fresh and drifted snow.
In particular on north-facing slopes above approximately 2800 m and generally in the Areas above approximately 3000 m (particularly glaciated areas).EAWS glossary, near-ground layers have become faceted. As demonstrated by avalanches that have been triggered, in these regions avalanches can start in the Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary and sometimes become large.
As a result of sunshine and warming temperatures during the day, gliding avalanches and loose snow avalanches are to be expected.
Weather review for Monday
Precipitation ended early on Monday morning. Towards the end of the precipitation the snowfall level dropped to 1500 m. During the day, conditions were mostly sunny with some low cumulus clouds.
Fresh snow
From Saturday evening until precipitation stopped on Monday morning, in the north above approximately 2500 m, in the south above approximately 2800 m:
- Avers, Val Bregaglia, Bernina region: 30 to 40 cm
- northern Alpine ridge, Grisons: 15 to 30 cm
- Less elsewhere
Temperature
At midday at 2000 m, around -1 °C in the north and +2 °C in the south
Wind
Strong during the night to Monday in the south and at high altitudes, elsewhere light to moderate northwesterly to northerly
Weather forecast to Tuesday
In the mountains conditions will be mostly sunny and very mild. The zero-degree level will rise to 3600 m.
Fresh snow
-
Temperature
At midday at 2000 m, around +8 °C in the north and +6 °C in the south
Wind
Light
Outlook
Apart from sometimes dense cloud cover, conditions will be mostly sunny in the mountains on Wednesday and Thursday. It will remain very mild. The zero-degree level will be between 3400 m and 3800 m. The southwesterly wind will be light to moderate.
Avalanche risk will decrease.