Central Prealps
Gersau
Manageable day. Moderate, with wind slab at the surface — the evidence is there to read before you commit to a slope.
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.
Snowpack & Weather
Snowpack
Fresh snow and wind are forming medium-sized snowdrift accumulations in the west and north, and generally smaller ones elsewhere. Below this, the top section of the Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary contains coarse-grained 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, primarily on north- and east-facing slopes at high altitudes.
Weather review for Wednesday
There were cloudy spells overnight in the west and south, while skies were quite clear in the east. It was rather sunny during the day.
Fresh snow
-
Temperature
At midday at 2000 m, between -1 °C in the north and +3 °C in the south
Wind
Light to moderate from westerly directions
Weather forecast until Ascension Day
The night will be rather cloudy. On Ascension Day it will be quite sunny along the Main Alpine Ridge in Upper Valais and in the Gotthard region, while elsewhere it will be very cloudy. Precipitation will be encountered over a wide area. The snowfall level will be between 1300 m in the north and 1800 m in the south.
Fresh snow
Until Ascension Day afternoon, the following amounts will fall above 2000 m:
- Extreme west of Lower Valais, Vaud and Fribourg Alps: 20 to 30 cm
- Other regions of Lower Valais and the northern flank of the Alps, Val Bregaglia and the Bernina region: 10 to 20 cm
- Less elsewhere
Temperature
At midday at 2000 m, between -3 °C in the north and +1 °C in the south
Wind
Southwesterly to westerly
- Strong on the northern flank of the Alps during the night
- Elsewhere light to moderate
Outlook
Friday
It will be very cloudy, with around 10 cm of snow falling over a wide area, less in Upper Valais and Ticino. The snowfall level will be around 1300 m. The wind will be mostly light.
The avalanche danger will not change significantly.
Saturday
In the north it will be very cloudy with 10 to 20 cm of snowfall over a wide area. The snowfall level will remain at around 1300 m. Along the Main Alpine Ridge and to the south of it, it will be mostly sunny with a strengthening northerly wind.
There will be a widespread increase in avalanche risk. In Upper Valais and Ticino, it will not change significantly.