Central Prealps
Gersau
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
The snowdrift accumulations that have formed in the last few days with sometimes strong northeasterly winds are still prone to triggering in places. With moderate winds from southwesterly directions, fresh snowdrift accumulations will form on Sunday, especially in the north at high altitudes.
Deeper in the Snow deposited on the ground in a multiplicity of layers.EAWS glossary, there are faceted 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 prone to triggering, especially on shady slopes above approximately 2400 m and generally in the Areas above approximately 3000 m (particularly glaciated areas).EAWS glossary. Avalanches may also be triggered in these deeper layers in places.
Outlook
In the west, 70 to 100 cm of new fallen snow is expected from Sunday evening to Tuesday evening. Up to 110 cm will fall locally, especially in the extreme west of Lower Valais on the border with France. On the central and eastern parts of the northern flank of the Alps, 40 to 60 cm of new fallen snow is expected, locally up to 70 cm. In Grisons and on the northern flank of the Alps, the amounts of new snow expected are appreciably smaller.
On Sunday evening, the snowfall level will increase rapidly to 1500 m, especially in the west, before dropping to 900 to 1100 m on Monday. On Tuesday, the snowfall level will drop to low altitudes. From Sunday evening to Monday evening, this event will be accompanied by strong to stormy westerly to southwesterly winds. During the night into Tuesday, the wind will shift to the northwest and will decrease.
With intense snowfall and stormy southwesterly winds, the avalanche danger will increase on Monday in the west and north, and significantly in the west. The extreme west of Lower Valais will reach danger level 4 (high) during the course of the day. In the regions exposed to heavier precipitation, more naturally triggered avalanches are to be expected. At high altitudes, these may also sweep away deeper, 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 of the Snow deposited on the ground in a multiplicity of layers.EAWS glossary and may occasionally become very large, especially on north-facing slopes. Exposed parts of transportation routes may be at risk. Snow will continue to fall on Tuesday, especially on the northern flank of the Alps. Danger level 4 (high) may also be reached in some regions along the northern Alpine ridge.