Mittelland and Jura
Vallon de Saint-Imier
Avalanche Problems
No distinct problem
1
Field notes
SLF uses this label when no single problem dominates the assessment, often on lower-danger days. It doesn't mean conditions are safe: any avalanche type is still possible, and normal caution applies. On stable days this is usually a signal to enjoy the mountains with general awareness; on less-stable days where the assessment is still inconclusive, it's a signal to be cautious specifically because there's no clear pattern to follow.
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
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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
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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.