Vaud Alps
Jaun
Day Risk Profile
Avalanche Problems
Persistent weak layers
2+
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.
Snowpack & Weather
Snowpack
Fresh and drifted snow from the last week is lying in many places on a faceted old snow surface or 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, especially on wind-protected shady slopes. The connection to the old snow surface is therefore poor in many places. South of a line from the Rhône to the Rhine, the entire Snow deposited on the ground in a multiplicity of layers.EAWS glossary is often faceted and loose. Here, avalanches may fracture down to near-ground layers. On the northern flank of the Alps, in Valais and in northern Grisons, avalanches may still become dangerously large. Many 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 remote triggering over larger distances are still being reported from Valais and northern Grisons. The probability of The abrupt release of a slab of snow on a mountain slope. After crack initiation and crack propagation in a weak layer the released slab comprises 3 elements: The weak layer, the gliding horizon and the slab. If the slope angle is steep enough, the slab will glide down. If the slope is not steep enough, the slab will settle down on the failed weak layer. Possibly a whumpf sound will follow due to air pressed out of the weak layer. The fracture line will be sharp edged.EAWS glossary being triggered remains high here and the situation requires patience.
With the mild weather, the snow became wet at low and intermediate altitudes.
Weather review for Wednesday
It was mostly sunny in the north, despite the high cloud cover. It was cloudy in the south, but mainly dry.
Fresh snow
-
Temperature
At midday at 2000 m, between +1 °C in the north and -2 °C in the south
Wind
Mostly moderate southwesterly
Weather forecast to Thursday
On Thursday it will be mostly sunny in the north. It will be very cloudy in the south and there will be a little light snowfall in some localities above 1300 m.
Fresh snow
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Temperature
At midday at 2000 m, between +1 °C in the north and -3 °C in the south
Wind
- Moderate and locally strong southwesterly winds
- There will be foehn winds in the valleys of the north during the course of the day.
Outlook to Saturday
There will be moderate to strong southwesterly winds and foehn winds in the valleys of the north.
It will be mostly sunny in the north on Friday, but only towards the east on Saturday. It will be very cloudy in the south on both days and snow will fall above approximately 1200 m. Up to 10 cm will fall on Friday. The amounts are still very uncertain for Saturday, especially from the Simplon region to the Valle Maggia.
Deeper layers of snow will stabilise only slowly due to the weak Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary, especially in areas south of a line from the Rhône to the Rhine. With the foehn wind, easily triggerable snowdrift accumulations will develop in the north from Friday and the avalanche risk will increase slightly.
In the south, the avalanche danger will increase slightly on Friday and appreciably on Saturday, depending on the amount of fresh snow.