Upper Valais
Leukerbad - Lötschental
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
In the last two days, new fallen snow and sometimes strong northeasterly winds have created snowdrift accumulations that are prone to triggering. These are sometimes large in the north, where the most snow fell (up to 50 cm), while in the other regions they are small to medium in size. Deeper in the Snow deposited on the ground in a multiplicity of layers.EAWS glossary, there are faceted 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 prone to triggering, especially on shady slopes above approximately 2400 m and generally in the Areas above approximately 3000 m (particularly glaciated areas).EAWS glossary. Avalanches may also be triggered in these deeper layers in places.
Outlook
Sunday
Clouds will gather rapidly in the west on Sunday, while it will remain sunny for longer in the east. The wind will shift to the west and will be strong in the north and west, moderate in the south. At 2000 m, the temperature will increase to around -2°C in the north and -6°C in the south. The avalanche danger will not change significantly. Fresh and somewhat older snowdrift accumulations will be prone to triggering in places. In addition, avalanches may be triggered in deeper layers of the Snow deposited on the ground in a multiplicity of layers.EAWS glossary, especially on north-facing slopes above 2400 m and in the Areas above approximately 3000 m (particularly glaciated areas).EAWS glossary.
Monday
Precipitation will set in from the west on Sunday evening. There will be widespread precipitation during the night and on Monday, heavy in the west. The snowfall level will be between 900 and 1300 m. In western Lower Valais and the Vaud Alps, 40 to 60 cm of snow will fall by Monday evening, 15 to 30 cm in the rest of Valais and on the northern flank of the Alps. There will be moderate to strong southwesterly winds. With new fallen snow and southwesterly winds, snowdrift accumulations will form that are prone to triggering. The avalanche danger will increase in the north, appreciably so in the west. Naturally triggered avalanches will be increasingly possible in the regions exposed to heavier precipitation in the west. In the east and south, the avalanche danger will not change significantly.