Western Prealps
Saint-Cergue
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.
Snowpack & Weather
Snowpack
With some new fallen snow and westerly winds, snowdrift accumulations have formed, some of which are prone to triggering. They are largest in the west, where the most snow fell.
Snow deposited on the ground in a multiplicity of layers.EAWS glossary structure is unfavourable in many locations in southern Valais, Ticino and Grisons, with distinct 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 in the middle and lower part of the snowpack that are prone to triggering. Reports of 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 avalanches triggered by human activity, some from a distance, are still being received from these regions. Snowpack structure is somewhat more favourable on the northern flank of the Alps and in northern Valais, but there are weak layers deeper in the snowpack in these regions too. These may still be triggered, especially where there is little snow and at transitions from a deep to shallow snowpack.
Weather review for Friday
A little snow fell in the south and west during the night. During the day, there were a few brighter intervals in the south, otherwise it snowed at times. The snowfall level was around 1400 m.
Fresh snow
From Thursday evening to Friday afternoon, the following amounts of fresh snow are expected above approximately 1600 m:
- extreme west of Lower Valais, northern Lower Valais: 15 to 25 cm
- Western part of the northern flank of the Alps, rest of Valais, southern Ticino: 5 to 10 cm
- Elsewhere: a few centimetres.
Temperature
At midday at 2000 m, around -2 °C
Wind
- Moderate at night, sometimes strong from the south on the Northern Alpine Ridge
- Moderate during the day in the north and in Valais, otherwise light westerly winds
Weather forecast to Saturday
A few centimetres of snow will fall in the north during the night. The snowfall level will be around 1200 m. In the late morning it will still be partly cloudy in the east, otherwise it will be quite sunny.
Fresh snow
A few centimetres in the north during the night
Temperature
At midday at 2000 m, around -2 °C
Wind
Light
Outlook for Saturday and Sunday
On Sunday it will be sunny at first. In the afternoon, clouds will gather from the west and in the south. On Monday it will be quite sunny in the north. A few snowflakes will fall on the southern flank of the Alps above approximately 1200 m. The wind will be mostly light on both days.
The avalanche risk will decrease, but only very slowly in southern Valais, Ticino and Grisons due to the distinct and 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.