Upper Engadine and Silvretta
Val S-charl
Hard-to-read day. Considerable, with wind slab and persistent weak layers in play — you can read the surface problem; the buried one sets the consequence.
Day Risk Profile
Avalanche Problems
Wind slab + Persistent weak layers
3-
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
With the sometimes strong Bise wind on Wednesday, some rather small but in some cases prone to triggering snowdrift accumulations will form, particularly along the Prealps and in the Jura. Otherwise, the large amounts of new snow and drifted snow in the north will slowly stabilise. In some places, however, the new snow of recent days is overlaid on 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 and in some cases also buried 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, particularly on shady slopes. In these weak layers, avalanches can be triggered, including large ones.
In the inneralpine regions of Valais and especially Grisons, 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 deeper in the Snow deposited on the ground in a multiplicity of layers.EAWS glossary are still prone to triggering in some places. Isolated avalanches may also be triggered in near-ground weak layers.
Weather review for Tuesday
Overnight to Tuesday, there was widespread snow down to low altitudes, with heavy snowfall in the north. During the day, the snowfall decreased appreciably. There were bright spells, particularly in southern Valais and Ticino.
Fresh snow
From Monday morning to Tuesday afternoon above approximately 1600 m:
- Northern Alpine Ridge from the Wildstrubel to the St. Galler Oberland: 50 to 70 cm
- Northern Alpine Ridge from the Rohneknie to the Wildstrubel, remaining central and eastern parts of the northern flank of the Alps, southern Goms, southern Tavetsch: 30 to 50 cm
- Remaining northern flank of the Alps and from southern Valais across northern Ticino to northern and central Grisons: 15 to 30 cm
- Less elsewhere, no snow in the south.
Temperature
At midday at 2000 m, between -9 °C in the north and -4 °C in the south
Wind
Strong from the north
Weather forecast to Wednesday
In the north, a few more centimetres of snow will fall during the night down to low altitudes. There will be bright spells during the day. In the west and south, it will be mostly sunny after a clear night.
Fresh snow
A few centimetres in the north.
Temperature
At midday at 2000 m, around -8 °C in the north and -3 °C in the south
Wind
- Remaining moderate to strong from the northeast during the night
- Light to moderate easterly wind during the day in the mountains; moderate to strong Bise wind along the Prealps and in the Jura
Outlook to Friday
In the west and south, it will be mostly sunny on both days. It will be partly cloudy along the Prealps and generally in the east. On Friday, light showers are possible in the east. In the mountains there will be a partly moderate northeasterly wind, with a moderate Bise wind in the Jura. The zero-degree level will rise to around 1600 m in the north and to 2200 m in the south.
The danger of dry avalanches will decrease. During the course of the day, moist loose snow avalanches from the loose snow and also gliding avalanches are to be expected.