Lower Valais
Génépi
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
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. Only in northern Lower Valais are snow depths approaching average.
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 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. It is possible for avalanches to be triggered in the old snowpack in these regions.
- In southern Lower Valais, Upper Valais, on the southern flank of the Alps and throughout Grisons, 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 are present 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 could be triggered in stability tests, it was very rare for avalanches to be triggered. Where fresh and somewhat older wind slabs lie on the weak snowpack, small avalanches are possible.
- The Snow deposited on the ground in a multiplicity of layers.EAWS glossary structure is more favourable in the extreme west of Lower Valais and northern Lower Valais and on the northern flank of the Alps. Below 2400 m, the snowpack has mostly frozen solid.
Weather review for Thursday
It was very cloudy in the south and on the Main Alpine Ridge in Valais. Some snow fell above 1000 m. Elsewhere, it was mostly sunny in the mountains.
Fresh snow
The following amounts of snow fell above 1400 m by Thursday afternoon:
- Main Alpine Ridge in Valais from the Monte Rosa to the Nufenen Pass, Val Bedretto, Valle Maggia: 15 to 30 cm
- Remaining central part of the Main Alpine Ridge in Valais directly along the border with Italy, remaining central part of the southern flank of the Alps, Upper Engadine, Val Bregaglia, Val Poschiavo, Aletsch region: 5 to 15 cm
- Elsewhere: fewer centimetres or dry.
Temperature
At midday at 2000 m, around -3 °C.
Wind
Southeasterly wind:
- Moderate at times in Grisons and on the southern flank of the Alps at high altitudes
- Elsewhere, strong during the night, storm-force in the Areas above approximately 3000 m (particularly glaciated areas).EAWS glossary, mostly moderate during the day
Weather forecast to Friday
Some snow will continue to fall in the south during the night. The snowfall level will be around 1000 m. During the day it will be sunny in the mountains.
Fresh snow
Until Friday morning:
- Monte Rosa to the Simplon region: 10 to 20 cm
- Southern Goms, Valle Maggia: 5 to 10 cm
- Elsewhere less or dry
Temperature
At midday at 2000 m, between +2 °C in the north and -2 °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 of the north, there will be a moderate south to southeasterly wind. Otherwise, the wind will be mostly light.
Outlook to Sunday
Conditions will be sunny in the mountains. The zero-degree level will increase to 3000 m. The wind will be mostly light.
The avalanche danger will decrease slowly in areas with new fallen snow, otherwise it will remain largely unchanged.