Lower Valais
Martigny-Verbier
Day Risk Profile
Avalanche Problems
Persistent weak layers
3=
Field notes
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
On the southern flank of the Alps and in Upper Engadine, the last six days’ fresh and drifted snow has been deposited on a weak Snow deposited on the ground in a multiplicity of layers.EAWS glossary, resulting in numerous medium-sized and indeed large spontaneous avalanches. In these regions, avalanches can still be triggered very easily in the Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary in many areas, including remotely. Avalanches are also to be expected deeper in the snowpack in the inneralpine regions of Valais and Grisons, especially on northern and eastern slopes. The avalanche situation requires patience.
North of a line from the Rhône to the Rhine, snowdrift accumulations, some of which are prone to triggering, have formed in recent days, and these are now covered with fresh snow. On Friday, the westerly winds will result in mostly small snowdrift accumulations. 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 deeper in the Snow deposited on the ground in a multiplicity of layers.EAWS glossary are less prone to triggering in these regions and such hazardous zones are rarer than in other regions.
Weather review for Thursday
In the south, precipitation ended during the night to Thursday, but only over the course of the day in the north. Conditions brightened up quickly in the west and south, while the east remained cloudy with light snowfall. The snowfall level dropped to between 600 and 1000 m.
Fresh snow
From Wednesday to Thursday afternoon, above approximately 1000 m:
- in the north 5 to 10 cm, locally up to 15 cm
- in the south and in Grisons 10 to 15 cm
In total, the following amounts have fallen above approximately 1500 m in the two days since midday on Tuesday:
- Jura, central part of the southern flank of the Alps, Upper Engadine, Val Bregaglia, Val Poschiavo: 20 to 40 cm
- otherwise a widespread 10 to 20 cm, with up to 30 cm in the far west
- northern flank of the Alps east of the Reuss, Prättigau, central parts of central Grisons: 5 to 10 cm
Temperature
At midday at 2000 m, around -6°C in the north and -3°C in the south
Wind
- Moderate to strong westerly to northwesterly at times in the north overnight, mostly light to moderate during the day
- Light to moderate northerly in the south, briefly moderate to strong northerly foehn wind in the morning
Weather forecast to Friday
In the west and north conditions will be mostly very cloudy with light precipitation from the morning onwards. The snowfall level will be between 600 and 1000 m. There will be sunny intervals on the Main Alpine Ridge in Valais and in the rest of Grisons, and it will be mostly sunny on the southern flank of the Alps and in Engadine.
Fresh snow
From Friday morning to Friday afternoon above approximately 1200 m:
- 5 to 10 cm in the west, with up to 15 cm in the far west of Lower Valais on the border with France and in the western Jura
- elsewhere less or dry
Temperature
At midday at 2000 m, around -4°C
Wind
- Freshening to moderate to strong westerly overnight in the west and north
- Light to moderate westerly to northwesterly in the south
Outlook to Sunday
On Saturday, conditions will be mostly cloudy in the west with light precipitation, especially in the Jura. The east will be very sunny at first, becoming increasingly cloudy as the day progresses. During the night to Sunday there will be some widespread precipitation in the west, with a total of 5 to 10 cm of snow falling above approximately 1200 m by Sunday morning. On Sunday, the north will be very sunny, with the west turning increasingly sunny. In the south, both days will be mostly sunny with broken cloud cover. Winds will be light to moderate from westerly directions.
There will be barely any change to the avalanche hazard on Saturday, but it will decrease somewhat in the north on Sunday. In inneralpine regions and in the south, avalanche hazard will decrease only very slowly due to the weak Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary. The situation for snow sports remains critical away from marked and open pistes.