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
There is appreciably less snow than usual at this time of year in most regions and snow conditions for ski touring are very poor in many places, especially below 2000 m and generally in the east.
The Snow deposited on the ground in a multiplicity of layers.EAWS glossary structure varies from region to region:
- On the Main Alpine Ridge in Valais and on the central southern flank of the Alps, fresh and drifted snow has been deposited on a thin but weak Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary 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, and avalanches may be triggered in the old snowpack in these regions.
- In the inneralpine regions of Valais, in northern Valais and throughout Grisons, 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 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 in the Snow deposited on the ground in a multiplicity of layers.EAWS glossary on shady slopes above approximately 2400 m. Although these weak layers have proven triggerable in stability tests, it is very rare for avalanches actually to be triggered. Where fresh and somewhat older snowdrift accumulations are lying on the weak snowpack, small avalanches are possible. On wind-protected shady slopes, the surface of the snowpack is faceted and loose.
- The Snow deposited on the ground in a multiplicity of layers.EAWS glossary structure is more favourable in western and northern Lower Valais and on the northern flank of the Alps. Below 2400 m, the snowpack has mostly frozen solid.
Weather review for Friday
Some snow continued to fall in the south during the night. The snowfall level was around 1000 m. During the day conditions were sunny in the mountains.
Fresh snow
In total, the following amounts fell above 1400 m between Wednesday afternoon and Friday morning:
- Main Alpine Ridge in Valais from Monte Rosa to the Nufenen Pass, Val Bedretto, Valle Maggia: 30 to 40 cm, in the Simplon region up to 50 cm
- remaining part of the Main Alpine Ridge in Valais directly along the border with Italy, remaining central part of the southern flank of the Alps: 10 to 20 cm
- Aletsch region, Main Alpine Ridge from the Nufenen pass to Upper Engadine: 5 to 10 cm
- elsewhere a few centimetres or dry
Temperature
At midday at 2000 m, between +3°C in the north and -1°C in the south
Wind
During the night to Friday in the Areas above approximately 3000 m (particularly glaciated areas).EAWS glossary and in the Alpine valleys in the north, moderate to strong, otherwise light to moderate south to southeasterly
Weather forecast to Saturday
After a clear night, conditions will be sunny in the mountains during the day.
Fresh snow
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Temperature
At midday at 2000 m, around +4°C
Wind
Overnight to Saturday in the Areas above approximately 3000 m (particularly glaciated areas).EAWS glossary and in the Alpine valleys in the north, moderate, sometimes strong south to southeasterly, elsewhere light to moderate
Outlook to Monday
Conditions will be sunny in the mountains. The zero-degree level will rise to 3200 m on Sunday and will be at 2600 m on Monday. Winds will be mostly light.
Avalanche danger will continue to decrease in areas with fresh snow, otherwise it will remain largely unchanged.