Upper Valais
Leukerbad - Lötschental
Hard-to-read day. Considerable, with new snow and persistent weak layers in play — you can read the surface problem; the buried one sets the consequence.
Day Risk Profile
Avalanche Problems
New snow + Persistent weak layers
3-
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
At high altitudes, the fresh and drifted snow from the last few days is lying on an Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary that contains coarse-grained 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 in its upper part, especially on north- and east-facing slopes.
As a result of solar radiation, moist snow slides from the new snow are to be expected. In many regions this is likely to occur on Tuesday afternoon, while in the northeast some may not happen until Wednesday.
Weather review for Tuesday
There was precipitation during the night, at times heavy in the north. In the morning there was still some precipitation in the northeast. Elsewhere, it was cloudy during the day with increasingly long bright spells. It was sunny in the south.
Fresh snow
From Monday afternoon until precipitation stopped on Tuesday, the following amounts fell above approximately 2200 m:
- North of a line from the Rhône to the Rhine and in the extreme west of Lower Valais: 20 to 40 cm
- Elsewhere: a widespread 10 to 20 cm, less in the south.
This means that, above approximately 2800 m, total snowfall since Sunday has been:
- Northern flank of the Alps west of Tödi, extreme west of Lower Valais, northern Valais and from Avers to the Bernina region: 40 to 50 cm
- Elsewhere: a widespread 20 to 40 cm, less in Ticino.
Temperature
At midday at 2000 m, between -5 °C in the north and 0 °C in the south
Wind
- Moderate and locally strong from the west
- On the Main Alpine Ridge and south of it, often strong from the northwest during the day
Weather forecast to Wednesday
During the night it will be mostly cloudy in the southwest and quite clear in the northeast. It will be quite sunny everywhere during the day.
Fresh snow
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Temperature
At midday at 2000 m, between +1 °C in the north and +4 °C in the south
Wind
- Mainly light at first
- In the afternoon, moderate in the north and generally at high altitudes, also locally strong winds, from westerly directions
Outlook to Friday
It will be mostly cloudy with longer bright spells on Thursday on the Main Alpine Ridge in Upper Valais and in the Gotthard region. Snow will fall at times, with the largest amounts in the far west, on the northern flank of the Alps and in the Bernina region, totalling around 20 to 30 cm. The snowfall level will be around 1300 m in the north and 1600 m in the south. On Thursday, there will be moderate and locally strong westerly winds in the north and at high altitudes. Winds will be light on Friday.
The danger of dry avalanches will increase in the far west, on the northern flank of the Alps and in the Bernina region, but will not change significantly in other regions. With the cool and often cloudy weather, only isolated wet avalanches are to be expected.