Prättigau and Davos
Westliche Silvretta
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
Precipitation set in last Saturday, initially in the south and later also in the north. Before this snowfall, conditions had been generally sunny and dry in the mountains for almost two weeks.
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 on shady slopes above around 2000 m and in Areas above approximately 3000 m (particularly glaciated areas).EAWS glossary, the fresh and drifted snow fell on a patchy continuous Snow deposited on the ground in a multiplicity of layers.EAWS glossary, otherwise on bare ground. On shady slopes above approximately 2400 m and generally in high Alpine regions, the fresh snow has fallen on pronounced 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, where avalanches can still easily be triggered.
Outlook
Precipitation will set in from the northwest overnight to Thursday. Thursday and Friday will be cloudy in the north, with occasional snowfall. By midday on Friday, 20 to 30 cm of snow is possible on the northern flank of the Alps and in the west of Lower Valais. Winds will veer from westerly to northeasterly. At high altitudes, winds will be light to moderate. There will be sunny intervals in southern Valais and on the southern flank of the Alps.
Avalanche risk will increase somewhat, especially over much of the northern flank of the Alps. There will be little change in other regions. Isolated avalanches may be triggered not only in fresh snowdrift accumulations but also in the Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary, especially on northern slopes above 2400 m and in Areas above approximately 3000 m (particularly glaciated areas).EAWS glossary.