Upper Engadine and Silvretta
Val dal Spöl
Day Risk Profile
Avalanche Problems
New snow + Persistent weak layers
4-
Field notes
New snow
Easy to spot - the snow is fresh. Look at recent avalanche activity in similar terrain, and pay attention to how much new snow has fallen in the last three days. Critical loading depends on temperature, wind, and what was on the surface before the storm. SLF advises waiting until the Snow deposited on the ground in a multiplicity of layers.EAWS glossary has had time to bond before committing to steep terrain in fresh snow.
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 west and north, many large and very large naturally triggered avalanches have occurred in recent days. There have also been some isolated extremely large avalanches in Valais. Natural avalanche activity decreased significantly on Wednesday. In the regions exposed to heavier precipitation in the west and north, this week's thick layers of new and drifted snow are gradually settling and consolidating. Naturally triggered very large avalanches are now possible only in isolated case. Fresh snow and westerly winds will result in widespread fresh snowdrift accumulations on Thursday.
This week's layers of fresh and drifted snow are thinner in Ticino, Grisons and some regions in southern Valais than they are further north and are lying on an unstable Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary with 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. Human activity can still very easily trigger avalanches, even over relatively large distances, in the old snowpack.
Weather review for Wednesday
After a break in the precipitation overnight to Wednesday, light precipitation set in in the west and north. The snowfall level was between 1000 and 1500 m. There were sunny intervals in the south and southeast.
Fresh snow
From Tuesday afternoon to Wednesday afternoon above approximately 1800 m:
- Lower Valais, northern Valais, northern flank of the Alps, Jura, northern Grisons, Lower Engadine a widespread 5 to 15 cm; central and eastern flank of the Alps up to 30 cm
- elsewhere a few centimetres; dry in the far south
Temperature
At midday at 2000 m, around -2 °C in the west and south, around -5 °C in the east
Wind
- In the north, moderate to strong northwesterly during the night and westerly to southwesterly during the day
- In the south, light to moderate northerly, backing southwesterly.
Weather forecast to Thursday
There will mainly be heavy cloud cover with widespread precipitation, centred in the far west and in the Upper Engadine. The snowfall level will be around 1000 m in the north and around 700 m in the south.
Fresh snow
From Wednesday evening to Thursday afternoon above approximately 1600 m:
- extreme west of Lower Valais, Vaud and Fribourg Alps, Moesano, Avers, Val Bregaglia, Corvatsch, Bernina region, Val Poschiavo: 20 to 30 cm
- elsewhere a widespread approximately 10 cm with up to 20 cm in eastern Ticino and Grisons
Temperature
At midday at 2000 m, around -3 °C
Wind
- Overnight to Thursday, moderate to strong southwesterly, temporarily foehn-like in the Alpine valleys
- Veering westerly to northwesterly over the course of the day, moderate to strong at high altitudes
Outlook to Saturday
On Friday, conditions will be cloudy in the north and 15 to 30 cm of snow will fall. The snowfall level will be between 600 and 900 m. The precipitation forecast is still uncertain. In the south, conditions will be sunny with a northerly wind and brighter in the inneralpine regions. There will be sunny conditions in Valais and the south on Saturday Elsewhere there will be broken cloud and a little precipitation will be possible. The snowfall level will rise to 1500 m. On both days, there will be a northwesterly wind, moderate to strong and occasionally storm-force at high altitudes.
Avalanche danger will decrease and hardly any very large naturally triggered avalanches are to be expected. In western and northern regions with a lot of snow, human activity may trigger avalanches, especially in the near-surface layers of the Snow deposited on the ground in a multiplicity of layers.EAWS glossary. In some regions in southern Valais, northern Ticino and Grisons, avalanche danger will decrease only very slowly due to the thin snow cover on the very weak Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary. In these regions, conditions for touring and off-piste skiing remain critical in many places.