Upper Engadine and Silvretta
Sur Tasna
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
With the new fallen snow and southerly wind, snowdrift accumulations will form, some of which are prone to triggering. These are little more prevalent and larger along the Main Alpine Ridge. Elsewhere, they are mostly small.
In some places, 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 that has been covered by snow is present in the uppermost section of the Snow deposited on the ground in a multiplicity of layers.EAWS glossary, particularly on shady slopes. In this 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 have continued to be triggered in recent days, especially in southern Valais and in Grisons.
In the 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 near the ground, isolated avalanches have continued to be triggered recently, especially in the inneralpine regions and southern parts of Grisons. In the other regions, there are still weak layers in the near-ground Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary in some places on shady slopes, but they are mostly so thickly covered that they are hardly prone to triggering.
Weather review for Saturday
During the night it was partly cloudy in the east and south, and outgoing longwave radiation was somewhat reduced. During the day there were some bright spells in the west, in Valais and in Grisons, while elsewhere it was mostly cloudy.
Fresh snow
-
Temperature
At midday at 2000 m, between 0 °C in the west and -2 °C in the east and south
Wind
Mostly light from northerly directions
Weather forecast to Sunday
During the night a little snow will fall over a wide area. During the day, snow will continue to fall, primarily in the west and in the south. During the day it will be quite sunny in the east. In the Bernese Oberland, in Valais and in the Engadine there will be increasing bright spells. In the south and in the far west it will often remain cloudy.
Fresh snow
From Saturday afternoon to Sunday afternoon, the following amounts of snow will fall above approximately 1500 m:
- Main Alpine Ridge in Upper Valais, directly on the border with Italy, western Ticino: 15 to 30 cm
- Extreme west of Lower Valais and remaining Main Alpine Ridge and to the south of it: 5 to 15 cm
- Elsewhere a widespread few centimetres
Temperature
At midday at 2000 m, around -2 °C in the north and -5 °C in the south
Wind
Moderate southerly wind along the Main Alpine Ridge and along the northern Alpine ridgeline. A moderate foehn wind in some places in the northern Alpine valleys, elsewhere mostly light
Outlook to Tuesday
On Monday it will be mostly cloudy from the Bernese Oberland to eastern Switzerland. A small amount of snow will fall in showers above approximately 1200 m. Elsewhere there will be prolonged bright spells. Conditions will be sunny in the south. On Tuesday it will be sunny after a clear night. On Monday, there will be a moderate northerly wind at high altitudes. On Tuesday the wind will be mostly light. The zero-degree level will be just below 2000 m on Monday and at 2000 m on Tuesday.
The avalanche danger will not change significantly for Monday. Particularly in the south, snowdrift accumulations prone to triggering will form with a northerly wind in some places. On Tuesday the avalanche danger will decrease. Wet and gliding avalanches are still hardly to be expected.