Churfirsten and Rhine Valley
Appenzeller Alpen
Hard-to-read day. Moderate, with wind slab and gliding snow in play — part of it readable at the surface, part of it buried and silent.
Day Risk Profile
Avalanche Problems
Wind slab
2-
Field notes
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.
Gliding snow
1
Field notes
Almost impossible to predict precisely, even when the warning signs are visible. A crack visible on the snowpack surface formed by snow-gliding on steep, and particularly grass-covered slopes. Areas below slopes with visible glide cracks should be avoided whenever possible due to threat of gliding sluffs or avalanches.EAWS glossary — gaps that open in the Snow deposited on the ground in a multiplicity of layers.EAWS glossary down to the ground — are often precursors to release, but they don't tell you when. A glide avalanche can release minutes after the cracks appear, or weeks later, or not at all. Some release without any visible warning. Avoid lingering anywhere near glide cracks: above them, alongside them, or below in the runout.
Snowpack & Weather
Snowpack
Near-surface layers on wind-protected shady slopes are lying 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 in places. During the course of this week, snowdrift accumulations have formed in winds from varying directions, with Wednesday's strong winds being from the southeast. The snowdrift accumulations are particularly prone to triggering on shady slopes.
In the inneralpine regions of Valais and Grisons, the layers of fresh and drifted snow are additionally lying on a weak Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary with pronounced near-ground 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. Avalanches can sometimes propagate into these deep weak layers or be triggered there directly in isolated cases. In other regions, weak layers in old near-ground Snow deposited on the ground in a multiplicity of layers.EAWS glossary still remain in places on shady slopes but are now mainly so thickly covered that they are largely insensitive to triggering.
Weather review for Wednesday
After a mainly clear night, conditions were mostly sunny, with broken cloud in the west and south. Cloud cover was thicker in places on the main Alpine ridge in Upper Valais. There was a light sprinkling of snow locally above around 1300 m, especially in the Simplon region.
Fresh snow
-
Temperature
At midday at 2000 m, around 0 °C in the west and south and -3 °C in the east.
Wind
- Moderate north to northeasterly during the night
- Veering moderate to strong southeasterly on Wednesday morning, occasionally strong to storm-force along the northern Alpine ridge
- Occasionally moderate to strong foehn wind in the foehn valleys of the north
- Strong bise wind in the Jura
Weather forecast to Thursday
After a clear night, conditions will be sunny in the mountains. Cumulus cloud will develop during the day along the Prealps.
Fresh snow
-
Temperature
At midday at 2000 m, around 0 °C in the north and -2 °C in the south
Wind
- Light to moderate northeasterly
- Light to moderate Bise wind in the Jura
Outlook to Saturday
Overnight to Friday, conditions will mostly be clear while during the day it will be sunny with broken cloud in the afternoon. There will be a light to moderate northeasterly wind. Overnight to Saturday, conditions will be partly cloudy, especially in the south, otherwise mostly clear. Variable cloud cover with sunny intervals and local showers is expected during the day. The snowfall level will be around 1200 m and the northeasterly wind will remain light to moderate. Saturday's weather conditions are, however, still uncertain.
The danger of dry avalanches will decrease. As daytime temperatures rise in the sunshine, the danger of wet avalanches will increase somewhat on steep sunny slopes over the course of each day. Isolated gliding avalanches will be possible.