Lower Valais
Val d'Hérens
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
- Westernmost Lower Valais, northern Valais, Vaud Alps: A lot of the new and drifted snow is prone to triggering. It lies on an Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary with 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 places in the central part of the Snow deposited on the ground in a multiplicity of layers.EAWS glossary. With the end of the precipitation on Friday morning, the naturally occurring The abrupt release of a slab of snow on a mountain slope. After crack initiation and crack propagation in a weak layer the released slab comprises 3 elements: The weak layer, the gliding horizon and the slab. If the slope angle is steep enough, the slab will glide down. If the slope is not steep enough, the slab will settle down on the failed weak layer. Possibly a whumpf sound will follow due to air pressed out of the weak layer. The fracture line will be sharp edged.EAWS glossary activity will be appreciably reduced. However, isolated naturally triggered avalanches may still become very large.
- Southern Valais, Ticino, Grisons: the Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary is very weak and contains distinct 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 the middle and lower part of the Snow deposited on the ground in a multiplicity of layers.EAWS glossary that are prone to triggering. Avalanches can easily be triggered by human activity in these layers and fractures in the snowpack can propagate over long distances. Avalanches may become very large, especially in southern Valais, where a lot of new snow and drifted snow is lying on the weak old snowpack from the last few days.
- Central and eastern parts of the northern flank of the Alps: there are also 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 the Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary in these regions. However, avalanches in these layers are less frequent and the main danger comes from the new and drifted snow. Below approximately 1800 m, the Snow deposited on the ground in a multiplicity of layers.EAWS glossary has been soaked by the sometimes intense rain.
Weather review for Thursday
Precipitation continued to fall in the west and north. Overnight to Thursday, the snowfall level was around 1800 m on the northern flank of the Alps and fell to 1200 to 1500 m in all regions during the day. In the Engadine, it was partly sunny in the late morning.
Fresh snow
From Wednesday afternoon to Thursday afternoon, the following amounts of fresh snow fell above approximately 2200 m:
- Westernmost Lower Valais, northern Valais: 40 to 60 cm;
- Rest of Valais, rest of northern Alpine ridge west of the Grimsel Pass: 20 to 40 cm
- Remaining western and central parts of the northern flank of the Alps, western Ticino: 15 to 30 cm; elsewhere less or dry.
In total, the following amounts of snow have fallen above 2200 m since the onset of precipitation on Tuesday:
- Westernmost Lower Valais, northern Lower Valais: 80 to 120 cm
- Vaud and Fribourg Alps, the rest of northern Lower Valais, the rest of the northern Alpine ridge west of the Grimsel Pass: 40 to 80 cm
- Remaining western and central parts of the northern flank of the Alps, western Ticino, southern Upper Valais: 30 to 50 cm
- Eastern part of the northern flank of the Alps, northern Grisons, rest of Ticino: 15 to 30 cm, less elsewhere
Temperature
At midday at 2000 m, around -2 °C
Wind
- Often strong southwesterly winds during the night
- During the day strong to storm force in the west and north, elsewhere moderate from west to northwest
Weather forecast to Friday
During the first half of the night, heavy precipitation will continue to fall in the north. The snowfall level will be between 1000 and 1200 m. In the late morning, it will initially be quite sunny in all regions before clouds move in from the west.
Fresh snow
From Thursday afternoon to Friday morning above 1600 m:
- Western Jura, westernmost Lower Valais, northern Alpine ridge from Les Diablerets to the Tödi: 15 to 25 cm
- Rest of Lower Valais, rest of the northern flank of the Alps, northern Grisons: 10 to 15 cm
- Elsewhere less, dry along the central southern flank of the Alps
Temperature
At midday at 2000 m, around -2 °C
Wind
- Strong to storm force from the northwest during the night
- During the day moderate to strong in the west at high altitudes, otherwise light to moderate from the southwest
Outlook to Sunday
On Saturday, it will be very cloudy in all regions and there will be some precipitation at times; in the south this will occur mainly during the night, while in the north it will be during the day. The snowfall level in the south will be around 1000 to 1200 m, while in the north it will drop down to low altitudes. On Sunday there will be some more precipitation in the north with sunny spells in the afternoon. Conditions will be quite sunny in the south. There will be a strong to storm force northerly wind in the south overnight to Sunday.
The avalanche danger will decrease in the west, but will not change significantly in the other regions.