Upper Valais
Leukerbad - Lötschental
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, the fresh and drifted snow that fell over Christmas 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. In the last few days, several avalanches, some of them large, have been triggered by human activity. Avalanches continue to be triggerable in the old snowpack in these regions.
- In central Valais, northern Upper Valais 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 have proven triggerable in stability tests, it is very rare for avalanches actually to be triggered. Small avalanches are possible where snowdrift accumulations from the last few days are lying on the weak snowpack. 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 the far west and northern parts of Lower Valais and on the northern flank of the Alps. Small snowdrift accumulations have formed locally. Below 2400 m, the snowpack has mostly frozen solid.
Weather review for Saturday
After a clear night, conditions were sunny and mild in the mountains.
Fresh snow
-
Temperature
At midday at 2000 m, around +5°C
Wind
During the night to Saturday in Valais and on the northern Alpine ridge, moderate to strong at times, otherwise light to moderate southeasterly
Weather forecast to Sunday
After a clear night, conditions will be sunny and mild in the mountains.
Fresh snow
-
Temperature
At midday at 2000 m, around +6 °C
Wind
Moderate during the night to Sunday at high altitudes, light to moderate northeasterly to easterly during the day
Outlook
Monday
Conditions will be sunny in the mountains. The zero-degree level will fall to 2600 m. Winds will be mostly light. Avalanche risk will decrease only slowly.
Tuesday
Conditions will be sunny in the mountains. The zero-degree level will fall to around 1000 m. The northerly wind will freshen and become moderate to strong. With fresh snow drift accumulations, avalanche danger will increase somewhat, especially on the Upper Valais Main Alpine Ridge and in Ticino.