Valais Chablais
Monthey-Val d'Illiez
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
The snow depths at intermediate and high altitudes are generally below average for the time of year. There is particularly little snow on the southern flank of the Alps. Only in parts of Lower Valais is snow depth roughly in line with the long-term average. On south-facing slopes and generally below 2400 m, the Snow deposited on the ground in a multiplicity of layers.EAWS glossary is mostly wet or crusted.
Along the Main Alpine Ridge and south of there, fresh and drifted snow was deposited at high altitudes on a thin but heavily faceted Snow deposited on the ground in a multiplicity of layers.EAWS glossary on Tuesday. Avalanches are particularly likely to be triggered in these regions.
North of the Main Alpine Ridge, there are pronounced 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, particularly on northern and eastern slopes above approximately 2400 m, but hardly any avalanches have been triggered there by human activity in recent days. At high altitudes, Tuesday’s strong southerly wind has transported some of the old snow, resulting in local snowdrift accumulations.
Weather review for Tuesday
Towards Tuesday morning, precipitation set in on the Main Alpine Ridge and south of there. The snowfall level was at around 1200 m. In other regions, it was mostly cloudy but dry.
Fresh snow
The following amounts had fallen above 1600 m by Tuesday afternoon:
- Main Alpine Ridge from the Grand St Bernard Pass to the Bernina and south of there: 5 to 15 cm, in western Ticino up to 20 cm
- elsewhere dry
Temperature
At midday at 2000 m, between +3°C in the north and -2°C in the south
Wind
From southerly directions:
- strong in northern regions exposed to the foehn wind and generally at high altitudes
- moderate at high altitudes on the southern flank of the Alps
Weather forecast to Wednesday
Overnight to Wednesday, some snow will continue to fall on the southern flank of the Alps above 1400 m. During the day, it will be mostly cloudy on the eastern part of the northern flank of the Alps, in Grisons and in Ticino, but elsewhere quite sunny.
Fresh snow
Between Tuesday afternoon and Wednesday morning, the following amounts are expected above 1600 m:
- Main Alpine Ridge from the Grand St Bernard Pass to the Bernina and south of there: 5 to 15 cm
- elsewhere dry
Overall between Tuesday morning and Wednesday morning above 1600 m:
- Main Alpine Ridge from Monte Rosa to the Nufenen Pass, western Ticino, Sotto Ceneri: 20 to 30 cm
- remaining Main Alpine Ridge of the Valais Alps and Main Alpine Ridge from the Nufenen Pass to the Bernina region, other regions of the central part of the southern flank of the Alps: 10 to 20 cm
- elsewhere dry
Temperature
At midday at 2000 m, around 0°C.
Wind
Rapidly subsiding southerly, light during the day
Outlook to Friday
On Thursday conditions will be very cloudy on the southern flank of the Alps, with sunny conditions elsewhere. Friday will be quite sunny everywhere. In the west, winds will be occasionally moderate and sometimes strong from the southwest, elsewhere light.
Avalanche risk will decrease slowly in the south but will otherwise remain largely unchanged.