Upper Engadine and Silvretta
Val Suot
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
In the north, the sometimes storm-force northerly winds have been transporting the large volumes of fresh snow and, towards the south in particular, also the Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary. This has resulted in all regions in snowdrift accumulations that are prone to triggering; in the north these accumulations are large. Fresh and drifted snow has been deposited on variable Snow deposited on the ground in a multiplicity of layers.EAWS glossary surfaces: on north-facing slopes, especially in sheltered locations, onto very loose snow, whereas up to high altitudes on south-facing slopes often onto a Layer of hard-compacted snow resulting from a melt-freeze process or wind.EAWS glossary. In many cases, the surface of the old snowpack has also been profiled by the wind and is irregular.
In the inneralpine regions of Valais and Grisons in particular, distinct 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 remain in near-ground layers of the Snow deposited on the ground in a multiplicity of layers.EAWS glossary. In addition, near-surface layers in locations sheltered from the wind contain snow-covered 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 which avalanches have repeatedly been triggered over the last week. Given the fresh snowfall, avalanches are again likely to be triggered with increasing frequency in the Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary in these regions.
Weather review for Thursday
There was heavy precipitation in the north. The snowfall level was around 500 m. There were sunny intervals in the far south.
Fresh snow
From Wednesday afternoon to Thursday afternoon, the following amounts fell above 1000 m:
- northern Alpine ridge, central part of the northern flank of the Alps: 40 to 70 cm
- rest of the northern flank of the Alps, southern Lower Valais, rest of northern Grisons: 20 to 40 cm
- Jura, southern Goms, rest of central Grisons, Engadine north of the Inn: 10 to 20 cm
- less elsewhere, dry in the far south
Temperature
At midday at 2000 m, around -9 °C in the north and -4 °C in the south
Wind
Strong, and in the Jura and at high altitudes sometimes storm-force, north to northwesterly, easing off somewhat in the afternoon in the north
Weather forecast to Friday
In the north, there will continue to be some widespread snowfall down to low altitudes until morning. Brighter periods will move in from the west over the course of the day. Conditions will be mosty sunny in southern Valais, Ticino and southern Grisons.
Fresh snow
From Sunday afternoon until precipitation stops around midday on Friday, the following amounts are expected above 1000 m:
- northern Alpine ridge: 10 to 20 cm
- rest of the northern flank of the Alps, southern Lower Valais, northern and central Grisons: 5 to 10 cm
- elsewhere less or dry
Temperature
Cold, at midday at 2000 m around -10 °C in the north and -4 °C in the south
Wind
- Strong to storm force northerly during the night
- Over the course of the day, the wind will veer northeasterly and will mainly be moderate to strong; there will be a strong Bise wind in the Jura and the western Prealps
Outlook
Saturday
After a clear night, conditions will initially be sunny on Saturday. Clouds will gather from the northwest in the afternoon. Conditions will remain sunny all day in the south and in Grisons. There will be light to moderate winds from northerly directions. The zero-degree level will rise to around 2000 m in the south, while in the north temperatures will remain cool with a zero-degree level of around 1200 m.
The danger of dry avalanches will fall in all regions. With solar radiation, moist snow slides are to be expected in the fresh snow during the day.
Sunday
There will be heavy cloud cover in the north on Sunday and there will be a widespread 5 to 15 cm of fresh snow down to low altitudes. Conditions will be quite sunny in the south. There will be an often moderate northeasterly wind which will become strong at times at high altitudes. There will be an increasingly strong Bise wind in the Jura and the western Prealps.
There will be no significant change in avalanche danger.