Lower Valais
Montana
Avalanche Problems
Wind slab
2-
Field notes
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.
Snowpack & Weather
Snowpack
There is appreciably less snow than usual at this time of year in most regions and snow conditions for ski touring are very poor in many places. Only in northern Lower Valais are snow depths approaching average. On southern slopes and in general below 2400 m, the Snow deposited on the ground in a multiplicity of layers.EAWS glossary has mostly frozen solid. On wind-protected northern slopes above approximately 2400 m, the surface of the snowpack is widely faceted.
On the Main Alpine Ridge in Valais and in western Ticino, the small volumes of fresh snow which have fallen in the last few days are lying on a thin but weak Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary of Snow grains, solid, with multiple flat glassy faces and sharp edges. Developed from faceting metamorphism, usually poorly bonded to one another (fewer contact points), a critical factor in avalanches if a faceted layer is covered with bonded snow. Typical grain size: 0.5 to 3 mm See also: www.snowcrystals.itEAWS glossary. With the expected arrival of fresh snow, the avalanche danger will increase rapidly in these regions. In the inneralpine regions of Valais, on the southern flank of the Alps and throughout Grisons, there are 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 of faceted crystals or Transparent, frequently flat crystals forming on the snowpack when moist air settles on the surface. It forms most often during cold, clear, humid nights. Once it is blanketed by fresh fallen snow, surface hoar is one of the most critical weak layer. See also: www.snowcrystals.itEAWS glossary in the Snow deposited on the ground in a multiplicity of layers.EAWS glossary on shady slopes above approximately 2400 m. Although these weak layers could be triggered in stability tests, it was very rare for avalanches to be triggered. Further north, the structure of the snowpack is more favourable.
Weather review for Wednesday
In the north, it was overcast with high stratus cloud up to around 2500 m with light snowfall down to low altitudes. Above that, it was sunny. In the south, it was still quite sunny in the morning, then increasingly cloudy, and snow began to fall in the afternoon.
Fresh snow
A few centimetres locally
Temperature
At midday at 2000 m, around -8 °C in the north, -3 °C in the south and -1 °C in the west
Wind
- Strong Bise wind in the Jura and the northern Prealps
- Otherwise mostly light easterly winds
Weather forecast to Thursday
In the south, it will be very cloudy, and snow will fall down to low altitudes. In the north, it will be sunny in the mountains.
Fresh snow
The following amounts of snow will fall above 1000 m by Thursday afternoon:
- Monte Rosa, upper Saas Valley, Simplon region, Binntal: 20 to 40 cm
- Rest of the Main Alpine Ridge directly along the border with Italy, Bedretto and Valle Maggia: 10 to 20 cm
- Northern neighbouring regions, Aletsch region, rest of Ticino, Moesano, Val Bregaglia and Bernina region: 5 to 10 cm
Temperature
At midday at 2000 m, between 0 °C in the north and -4 °C in the south
Wind
- Southeasterly winds, strong during the night, stormy in the Areas above approximately 3000 m (particularly glaciated areas).EAWS glossary
- Easing significantly during the day
Outlook to Saturday
On Friday morning, the snowfall will end in the south and it will then be widely sunny in the mountains. It will become increasingly mild.
The avalanche danger will decrease only slowly in areas with new fallen snow, otherwise it will remain largely unchanged.