Upper Valais
Turtmanntal
Day Risk Profile
Avalanche Problems
Persistent weak layers
2+
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
Near-surface layers on wind-protected shady slopes are lying on 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 places. There are continued reports of avalanches being triggered in this 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. Over the course of this week, snowdrift accumulations have formed with wind from varying directions, some of which are still prone to triggering in isolated cases.
In the inneralpine regions of Valais and Grisons, the layers of fresh and drifted snow are also lying on a weak Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary with pronounced near-ground 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. Avalanches can propagate into these deep weak layers in isolated cases or can be triggered directly in deep layers. In the other regions, there are still weak layers in the near-ground old snowpack in some places on shady slopes, but they are mostly so thickly covered that they are hardly prone to triggering.
Weather review for Friday
After a clear night, conditions were sunny.
Fresh snow
-
Temperature
At midday at 2000 m, between +3 °C in the west and -1 °C in the east
Wind
Light to moderate from north-easterly directions
Weather forecast to Saturday
The night will be partly cloudy and outgoing longwave radiation somewhat reduced. During the day it will initially be fairly sunny; as the day progresses it will become increasingly cloudy and isolated showers are possible.
Fresh snow
-
Temperature
At midday at 2000 m, around -1 °C in the west and -3 °C in the east
Wind
Mostly light, with a sometimes moderate northerly wind in the afternoon.
Outlook to Monday
During the night into Sunday, snow will fall over a wide area; on Sunday morning, some snow will fall, mainly in the south and west. The snowfall level will be below 1000 m. On the southern flank of the Alps, 15 to 30 cm of snow is expected, further north 5 to 15 cm. The wind will be light to moderate from southerly directions on Sunday and northerly directions on Monday. The danger of dry avalanches will increase significantly in the south. In the north, the avalanche danger will not change significantly.