Lower Valais
Val d'Hérens
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
On the northern flank of the Alps and in western and northern Lower Valais, the surface of the Snow deposited on the ground in a multiplicity of layers.EAWS glossary on wind-protected shady slopes was often faceted and loose, especially at high altitudes. Here, it was a weak base for the fresh and drifted snow. Elsewhere, the surface of the snowpack has often been shaped by the wind and was often frozen solid, especially on the northern flank of the Alps below 2400 m.
In the other regions, the thin Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary mostly consists 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 with embedded crusts. Where drifted snow is lying on this weak old snowpack, it can be easily triggered in places. In addition, individual avalanches may still be triggered in the old snowpack, especially on the Main Alpine Ridge in Valais and on the central part of the southern flank of the Alps.
Weather review for Saturday
During the night to Saturday, some snow fell on the northern flank of the Alps, in the Gotthard region and in northern Grisons. During the day, it was mostly sunny in Valais, on the southern flank of the Alps and in Grisons, but still mostly cloudy on the northern flank of the Alps.
Fresh snow
Snow fell down to low altitudes. Snowfall at altitude:
- Glarus Alps to Alpstein region: 20 to 40 cm
- Central and remaining eastern parts of the northern flank of the Alps: 10 to 20 cm
- Rest of the northern flank of the Alps, Gotthard region, northern Grisons: 5 to 10 cm
- Elsewhere less or dry
Temperature
At midday at 2000 m, between -10 °C in the north and -6 °C in the south
Wind
Westerly winds, during the night often strong on the northern flank of the Alps and in Valais, otherwise mostly moderate
Weather forecast to Sunday
During the night to Sunday it will be partly cloudy in the east and a little snow will fall on the eastern part of the northern flank of the Alps. During the day it will be sunny everywhere.
Fresh snow
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Temperature
At midday at 2000 m, around -9 °C
Wind
From the northwest
- Still moderate during the night, especially in the Bernese Oberland and along the Main Alpine Ridge
- Otherwise light
Outlook until Tuesday
On Monday and Tuesday it will be mostly sunny but cold in the mountains. The northerly wind will be mostly light on Monday, and often moderate on Tuesday along the Main Alpine Ridge.
The unfavourable Snow deposited on the ground in a multiplicity of layers.EAWS glossary structure means that avalanche risk will decrease only very slowly.