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Upper Valais

Turtmanntal

Sat 27 Dec

Avalanche Problems

Moderate (2-), lower end of the band Dry avalanches · all day
Dry snow level 2 Persistent weak layers 2-
N, NE, E, W, NW
above 2400m
The small wind slabs of the last two days are lying on top of a weakly bonded Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary on shady slopes. Avalanches can in isolated cases be released by people and reach medium size. Backcountry touring calls for careful route selection. The Avalanche Warning Service currently has only a small amount of information that has been collected in the field, so that the avalanche danger should be investigated especially thoroughly in the relevant locality.
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.

Source: SLF Avalanche Bulletin Interpretation Guide

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

-

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.

Source

SLF

Issued

27 Dec 06:21 UTC

Valid until

27 Dec 16:00 UTC

Next update

27 Dec 16:00 UTC

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