Central Grisons and Anterior Rhine
Domleschg - Lenzerheide
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
Fresh and drifted snow has been deposited on a surface of loose fresh snow and sometimes 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 (hoar frost), particularly on slopes protected from the wind. The avalanche danger will increase significantly as the snowfall becomes more intense and also as a consequence of the warmer temperatures in the afternoon in the west and north. With the rain, more wet and gliding avalanches are also to be expected. This will apply in the west from Sunday lunchtime and in the other regions of the north from Sunday evening.
On shady slopes above approximately 2400 m and in the Areas above approximately 3000 m (particularly glaciated areas).EAWS glossary in general, there are faceted 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 deep in the Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary. After hardly any avalanches were triggered in these layers in the last few days, this may be possible again from Sunday afternoon due to the fresh snow and rising temperatures.
Weather review for Saturday
It was quite sunny on the Main Alpine Ridge, in the south and in Grisons. Elsewhere it was mostly cloudy but mainly dry.
Fresh snow
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Temperature
At midday at 2000 m, around +1 °C
Wind
There was a moderate to strong southwesterly wind. In Grisons and Ticino, the wind was light to moderate
Weather forecast to Sunday
It will be very cloudy with light precipitation at first, becoming heavier in the afternoon from the west. The snowfall level will be around 1500 m and will rise a little during the day to 2200 m in the west.
Fresh snow
By Sunday afternoon, the following amounts of snow will fall above approximately 2400 m in the west and 1800 m in the east:
- Northern flank of the Alps west of the Reuss, Valais not including Goms: 20 to 30 cm.
- Eastern part of the northern flank of the Alps east of the Reuss, Goms, rest of the Gotthard region: 10 to 20 cm
- Grisons, Ticino not including the Gotthard region: less than 10 cm, dry in the very south
A little snow will fall in the Jura, followed by rain
Temperature
At midday at 2000 m, around +1 °C
Wind
There will be a westerly wind that will be:
- Strong in the north and at high altitudes in general, storm force at times in the west
- Moderate in Grisons
Outlook until Tuesday
Monday
Intense precipitation will fall in the north on Sunday evening, accompanied by storm force westerly winds. The snowfall level will increase to 2200 m. Above approximately 2400 m, a further 20 cm of fresh snow is expected on the northern flank of the Alps, with 10 cm less expected in the west. On Monday, it will be sunny and mild and the wind will ease.
During the night, the danger of dry avalanches will increase further at high altitudes, appreciably so in the east. Below approximately 2200 m, wet and gliding avalanches are to be expected with the rain. During the day, the avalanche danger will decrease below approximately 2200 m, but will not change significantly at higher altitudes. On steep sunny slopes, moist snow slides from the fresh snow are also possible at high altitudes.
Tuesday
It will be quite sunny and mild. The zero-degree level will increase to 3400 m. The southwesterly wind will be light to moderate.
The danger of dry avalanches will gradually decrease. Gliding avalanches are still possible on steep grassy slopes. In addition, moist snow slides from the fresh snow are possible on steep sunny slopes, even at high altitudes.