Upper Engadine and Silvretta
Val S-charl
Day Risk Profile
Avalanche Problems
Wind slab + Persistent weak layers
2+
Field notes
Wind slab
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.
Persistent weak layers
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
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. Some of the snowdrift accumulations are still prone to triggering.
In the inneralpine regions of Valais and Grisons, the layers of fresh and drifted snow are also 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 propagate into these deep weak layers in isolated cases or can be triggered directly in deep layers. In the other regions, there are still weak layers in the near-ground old snowpack in some places on shady slopes, but they are mostly so thickly covered that they are hardly prone to triggering.
Weather review for Thursday
After a clear night, it was mostly sunny.
Fresh snow
-
Temperature
At midday at 2000 m, between +3 °C in the west and -1 °C in the east
Wind
From southeast to east
- Moderate to strong overnight, especially on the northern Alpine ridge
- Mostly light during the day
Weather forecast to Friday
After a clear night, it will be mostly sunny in the mountains. Over the course of the day, cumulus clouds will form, especially in the Prealps.
Fresh snow
-
Temperature
At midday at 2000 m, around 0 °C in the west and -2 °C in the east
Wind
Mostly light from northeasterly directions
Outlook to Sunday
In the north, it will be quite sunny on Saturday and partly sunny on Sunday. Over the second half of both days, cumulus clouds will form and isolated showers will be possible, although the amounts of precipitation will be small. The snowfall level will be around 1200 m. In the south, it will still be quite sunny on Saturday morning, and mostly overcast on Saturday afternoon and Sunday. Above 1000 to 1200 m, some snow will fall, especially during the night into Sunday and on Sunday morning. At present, around 10 to 15 cm of fresh snow is expected in the south, but the model forecasts are still very uncertain.
The danger of dry avalanches will generally continue to decrease. It may increase slightly, and temporarily, in the south on Sunday. Isolated wet snow slides and wet avalanches are still to be expected, especially from steep sunny slopes, but this activity will tend to be small and the avalanches will be mostly superficial.