Central Grisons and Anterior Rhine
Domleschg - Lenzerheide
Avalanche Problems
Persistent weak layers
1
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 northern flank of the Alps, the fresh and drifted snow which has fallen over the last week on high-altitude wind-protected shady slopes is lying on an often faceted and therefore weak old snow surface. Elsewhere, the snow surface has often been shaped by the wind and is frequently frozen solid below 2400 m.
In western and northern Lower Valais, the Snow deposited on the ground in a multiplicity of layers.EAWS glossary structure is relatively favourable.
In other regions, the Snow deposited on the ground in a multiplicity of layers.EAWS glossary is thin and weak, and mostly consists 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 embedded crusts. Snowdrift accumulations deposited on top of this snowpack are in some cases triggerable. In addition, isolated avalanches in the Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary close to the ground cannot be ruled out, especially on the Main Alpine Ridge in Upper Valais and on the central part of the southern flank of the Alps. However, no more such avalanches have been reported in the last week.
Weather review for Tuesday
It was sunny and cold in the mountains.
Fresh snow
-
Temperature
At midday at 2000 m, around -12 °C in the north and -8 °C in the south
Wind
Northerly wind:
- Moderate to strong along the Main Alpine Ridge and to the south of it
- Elsewhere mostly light
Weather forecast to Wednesday
In the mountains it will be sunny and remain cold.
Fresh snow
-
Temperature
At midday at 2000 m, around -12 °C
Wind
Northwesterly wind:
- Moderate on the Main Alpine Ridge and to the south of it, sometimes strong in the afternoon at higher altitudes
- Elsewhere light to moderate
Outlook to Friday
There will be widespread precipitation on Thursday and Friday, which will be intense in the west and north from Thursday afternoon. In the extreme west of Lower Valais and northern Lower Valais, a total of 60 to 80 cm of snow is expected to fall; in the rest of Valais and on the northern flank of the Alps, 30 to 60 cm is expected. The snowfall level will increase temporarily to 1600 m in the west and north overnight to Friday, and will remain at low altitude elsewhere. The snowfall will be accompanied by a strong to storm-force westerly wind.
The avalanche danger will increase significantly in the west and north. Danger level 4, high, is expected to be reached in Lower Valais on Friday. The avalanche danger will also increase slightly in Grisons, but will not change significantly in the south.