Lower Valais
Val d'Anniviers
Day Risk Profile
Avalanche Problems
Wind slab + Persistent weak layers
3-
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
Over the last two days, lots of snow has fallen in the north down to low altitudes. This snow has been transported significantly by sometimes stormy northerly winds and also by the Bise wind on Friday. In the south, it was mainly looser old snow that was transported. This has resulted in snowdrift accumulations in all regions; in the north these accumulations are large. On wind-protected north-facing slopes, fresh and drifted snow is lying on very loose snow. On south-facing slopes, meanwhile, it is often lying on a Layer of hard-compacted snow resulting from a melt-freeze process or wind.EAWS glossary up to high altitudes. In many cases, the surface of the Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary has also been shaped by the wind and is irregular.
In the upper part of the Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary, in locations sheltered from the wind there is a burried 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 layer in which avalanches may still be triggered. In the inneralpine regions of Valais and in Grisons in particular, avalanches are also possible in 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 near the ground.
Weather review for Friday
During the night, there was widespread snowfall down to low altitudes, but only isolated snowfall in the northeast during the day. During the course of the day, it was quite sunny in the far west, in Valais and in the south.
Fresh snow
From Thursday afternoon until precipitation stopped on Friday, the following amounts fell above 1000 m:
- Northern flank of the Alps east of the Wildstrubel, northern Lower Valais: 15 to 30 cm
- less elsewhere; dry in the south.
In total, the following amounts of snow have fallen since the onset of precipitation on Wednesday afternoon:
- Northern flank of the Alps east of the Gemmi Pass: 80 to 110 cm
- Northern Alpine ridge west of the Gemmi Pass: 50 to 80 cm
- Other regions of the western part of the northern flank of the Alps and of western Lower Valais, northern Grisons: 30 to 50 cm
- Elsewhere a widespread 10 to 30 cm; dry in the far south
Temperature
At midday at 2000 m, between a cold -10 °C in the north and -6 °C in the south
Wind
- Northerly winds, moderate on the northern flank of the Alps, otherwise strong to stormy, easing somewhat over the course of the day
- Moderate Bise wind in the western Prealps and the Jura
Weather forecast to Saturday
After a clear night, conditions will initially be sunny on Saturday. Clouds will gather from the northwest in the afternoon, and the first snowflakes will fall in the Jura. It will remain sunny in the south and in Grisons.
Fresh snow
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Temperature
Less cold, at midday at 2000 m between -4 °C in the north and +1 °C in the south
Wind
Light to moderate from northerly directions
Outlook
Sunday
There will be heavy cloud cover in the north and a widespread 10 to 20 cm of snowfall down to low altitudes. It will be quite sunny in Valais and the south. The northeasterly wind will be mostly moderate. A strong Bise wind will rise in the Jura and the western Prealps.
The avalanche danger will not change significantly in the north and will decrease in the south.
Monday
After the weather calms during the night, on Monday strong northwesterly winds will set in as the day progresses as well as intense snowfall in the north. The snowfall level will remain at low altitudes. It will be quite sunny in the far south.
The avalanche danger will increase significantly in the north in the afternoon. There will be no significant change in the south.