Upper Engadine and Silvretta
Val dal Spöl
Avalanche Problems
Persistent weak layers
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Field notes
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, especially below 2000 m and generally in the east.
Snow deposited on the ground in a multiplicity of layers.EAWS glossary structure is variable from region to region:
- On the Main Alpine Ridge in Valais and on the central southern flank of the Alps, last week’s 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. A few avalanches, some large, have been triggered by human activity over the last few days. Isolated avalanches may still be triggered in the old snowpack in these regions. Sunday’s northeasterly winds have produced snowdrift accumulations, some prone to triggering, especially adjacent to ridgelines.
- 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 some of these weak layers have proven triggerable in stability tests, very few avalanches have actually been triggered. Small avalanches are possible where the last few days’ snowdrift accumulations are lying on the weak snowpack. On wind-protected shady slopes, the surface of the snowpack is faceted and loose.
- Snow deposited on the ground in a multiplicity of layers.EAWS glossary structure is more favourable in the westernmost 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 Sunday
After a clear night, conditions were sunny and very mild in the mountains.
Fresh snow
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Temperature
At midday at 2000 m around +6°C in the north and east and around +8°C in the south.
Wind
Moderate northeasterly to easterly, easing somewhat over the course of the day.
Weather forecast to Monday
After a clear night, conditions will be sunny and mild in the mountains.
Fresh snow
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Temperature
At midday at 2000 m, around +4°C
Wind
Light to moderate from westerly directions
Outlook
Tuesday
Conditions will be sunny in the mountains. The upper limit for low stratus cloud will rise to between 1400 and 1700 m in the north. The zero-degree level will drop to around 1800 m in the west and south and towards 1000 m in the north and east. The northerly wind will freshen, becoming moderate to strong. Moderate Bise wind in the Prealps. Freshly drifted snow will somewhat increase avalanche risk, especially on the Main Alpine Ridge in Upper Valais and in Ticino.
Wednesday
Conditions will be sunny in the mountains. The Bise wind and foehn wind from the north will ease. There will be a moderate northerly wind at high altitudes. There will be hardly any change in avalanche risk.