Upper Engadine and Silvretta
Sur Tasna
Hard-to-read day. Considerable, with wet snow, 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
Wet snow
3
Field notes
Rolling snowballs, deep penetration when you step or ski, and small natural slides are clear signals that the Snow deposited on the ground in a multiplicity of layers.EAWS glossary is losing strength. After a clear, cold night the surface often freezes into a strong supporting Layer of hard-compacted snow resulting from a melt-freeze process or wind.EAWS glossary, and conditions are favourable in the early morning. After a warm, overcast night, the problem may be present from the start of the day. Plan early returns and watch the runout zones below you.
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 mild weather, partly overcast nights and occasional rain, moistening of the Snow deposited on the ground in a multiplicity of layers.EAWS glossary continued over the course of last week. On south-facing slopes the snowpack is water-saturated up to around 3000 m, and on east- and west-facing slopes up to 2500 to 2700 m, while on north-facing slopes it is water-saturated below 2000 m, with moistening progressing between 2000 and 2400 m.
Given the expected volumes of fresh snow, heavy at times in the south, large snowdrift accumulations will form at high altitudes. On north-facing slopes in particular, naturally triggered avalanches may sweep away the entire Snow deposited on the ground in a multiplicity of layers.EAWS glossary, especially in regions exposed to heavier precipitation in Valais, but occasionally also in other regions. In addition, avalanches in the fresh and drifted snow may be triggered by human activity.
With the rain, more wet and gliding avalanches are also to be expected.
Weather review for Sunday
Conditions were mostly cloudy, with light showers in the Prealps. The snowfall level was around 2000 m. There were brighter intervals in Grisons.
Fresh snow
-
Temperature
At midday at 2000 m, around +3 °C in the north and in Ticino and +6 °C in the inneralpine regions
Wind
Light to moderate southerly, increasing to moderate to strong on the northern Alpine ridge during the course of the day
Weather forecast to Monday
On Sunday evening precipitation will set in in the south, becoming heavier overnight to Monday, with some regions of the south seeing very heavy precipitation. The precipitation will also spread to northern regions, but will be lighter there. The snowfall level will be around 1800 to 2000 m, falling to 1500 to 1700 m by Monday morning in the regions exposed to heavier precipitation on the main Alpine ridge in Upper Valais.
Fresh snow
By Monday afternoon above 2200 to 2400 m:
- Monte Rosa region, Saas Valley, Simplon region: 60 to 80 cm
- rest of main Alpine ridge in upper Valais, northwest Ticino: 40 to 60 cm
- rest of main Alpine ridge from the Great St. Bernard Pass to the Lukmanier Pass, northern Alpine ridge from the Lötschental to the Reuss, lower Valle Maggia, Valle Leventina: 20 to 40 cm
- rest of Valais, rest of northern Alpine ridge west of Tödi, main Alpine ridge from the Lukmanier Pass to the Bernina region: 15 to 30 cm
- elsewhere a few centimetres or dry
Temperature
At midday at 2000 m, around +2 °C in the west and south and +4 °C in the east
Wind
Strong south to southeasterly overnight to Monday in the Areas above approximately 3000 m (particularly glaciated areas).EAWS glossary, elsewhere moderate to strong, dying down in the afternoon
Outlook
Tuesday
Conditions will be very cloudy with light precipitation. The snowfall level will be around 1500 to 1800 m in the north and 1800 to 2000 m in the south. As the day progresses it will brighten up, especially in Valais and in the south. There will be a light to moderate northeasterly wind.
The danger of dry avalanches will decrease in the south. However, off-piste skiing conditions will remain critical at high altitudes. In the north, there will be hardly any change in dry avalanche danger. Wet avalanches are possible in all regions, especially on west-, north- and east-facing slopes below approximately 2400 m. In the regions with fresh snow, loose snow avalanches are to be expected in the fresh snow at high altitudes with the warmth from the sun, and also moist snow slides and glide snow avalanches at intermediate altitudes.
Wednesday
Conditions will be quite sunny, with a possibility of isolated light showers over the course of the day. The zero-degree level will rise to 2800 m. Winds will mostly be light. The danger of dry avalanches will decrease. The danger of wet avalanches will increase during the day.