Central Grisons and Anterior Rhine
Albulatal
Avalanche Problems
Persistent weak layers
2-
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
In northern Lower Valais, there is somewhat more snow at high altitudes than is usual at this time of year. Elsewhere, the snow depths are below average. On southern slopes and generally below 2400 m, the Snow deposited on the ground in a multiplicity of layers.EAWS glossary is mostly wet or has frozen solid.
On the Main Alpine Ridge and to the south of it, this week’s fresh snow is lying at altitude 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.
North of the Main Alpine Ridge, small wind slabs have formed at altitude in some regions. Some of them lie on 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 (hoar frost) and can still be triggered as avalanches. In addition, in the inneralpine regions of Valais and throughout Grisons in particular, there are some 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 deeper in the Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary, especially on northern and eastern slopes above approximately 2400 m. However, hardly any avalanches have been triggered in these layers for some days.
Weather review for Friday
In Valais and Sotto Ceneri there were some clear spells, otherwise it was mostly cloudy.
Fresh snow
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Temperature
At midday at 2000 m, between +3 °C in the north and 0 °C in the south
Wind
- Moderate to strong from southerly directions during the night
- Light to moderate from the southwest during the day
Weather forecast to Saturday
It will be quite sunny in the mountains in the the north and in the Engadine. It will often be cloudy on the central part of the Main Alpine Ridge and on the central part of the southern flank of the Alps.
Fresh snow
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Temperature
At midday at 2000 m, around +2 °C
Wind
Often light. Moderate southerly wind at times on the Main Alpine Ridge
Outlook
On Sunday and Monday, it will be partly sunny and mild in the north. The southerly wind will be strong on Sunday and moderate to strong on Monday. In the Alpine valleys, there will be a strong foehn wind at times. In the south, snow will fall at times above approximately 1300 m. By Monday evening, 20 to 40 cm of new snow is expected on the Main Alpine Ridge in Upper Valais and 10 to 20 cm on the Main Alpine Ridge in the rest of Valais and in Ticino.
The avalanche danger will increase in the south with the arrival of new snow. It will not change significantly in the other regions.