Prättigau and Davos
Südliches Prättigau
Day Risk Profile
Avalanche Problems
Wind slab + Persistent weak layers
3+
Field notes
Wind slab
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.
Persistent weak layers
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
- Westernmost Lower Valais, northern Valais, Vaud Alps: the considerable amount of new and drifted snow resulting from the intensive precipitation of the past few days is still prone to triggering in places. This snow lies on an Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary whose central section contains 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 in some parts. Avalanches can be triggered mainly at transitions from a shallow to a deep Snow deposited on the ground in a multiplicity of layers.EAWS glossary.
- Southern Valais, Ticino, Grisons: the Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary is very weak and contains distinct 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 in the middle and lower part of the Snow deposited on the ground in a multiplicity of layers.EAWS glossary that are prone to triggering. Avalanches can easily be triggered by human activity in these layers and fractures in the snowpack can propagate over long distances. Avalanches may be very large, especially in southern Valais. Here, the new and drifted snow of the last few days has formed into a very unfavourable combination of layers on top of the weak old snowpack.
- Central and eastern parts of the northern flank of the Alps: there are also 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 in some parts of the Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary in these regions. However, avalanches are triggered less frequently in these layers. Below approximately 1800 m, the Snow deposited on the ground in a multiplicity of layers.EAWS glossary has been soaked by the rain.
- Prealps: newer snowdrift accumulations lie on a mostly favourable Snow deposited on the ground in a multiplicity of layers.EAWS glossary, but are still prone to triggering in places.
Weather review for Saturday
It was very cloudy and there was some precipitation at times, falling as snow above approximately 1200 m.
Fresh snow
From Friday to Saturday evening above 1400 m:
- Westernmost Lower Valais, Vaud Alps, Simplon region, western Ticino: 10 to 15 cm
- Elsewhere a widespread few centimetres
Temperature
At midday at 2000 m, around -2 °C
Wind
- Moderate to strong southerly winds during the night
- Light during the day, increasingly moderate towards the evening from the north
Weather forecast to Sunday
During Sunday night into Monday, some more snow will fall in the north down to low altitudes. The precipitation will end in the early morning and there will be sunny spells in the afternoon. It will be dry and quite sunny in the south.
Fresh snow
From Saturday evening to Sunday morning:
- Northern flank of the Alps 10 to 15 cm, locally more
- Elsewhere a few centimetres over a wide area; dry in the south
Temperature
At midday at 2000 m -6 °C in the north and -1 °C in the south
Wind
- There will be a moderate northerly wind during the night, which will be strong along the Main Alpine Ridge and south of it
- Moderate during the day, strong towards the evening from westerly directions
Outlook to Tuesday
From Sunday evening onwards, a significant northwesterly trend will set in, bringing heavy snowfall to the northern flanks of the Alps and Valais. The snowfall level will rise temporarily to 1400 m overnight to Monday and fall below 1000 m on Monday; on Tuesday it will be between 500 and 800 m. By Tuesday evening, between 70 and 110 cm of snow is expected to fall in the regions exposed to heavier precipitation in western Valais and on the northern Alpine ridge, and even more in some localities. Otherwise, around 60 cm of snow is expected to fall, except in the south. There will be a strong to storm force westerly wind.
On Monday, the avalanche danger will increase to danger level 4 (high) as a result of the intense precipitation and the storm force westerly winds on the northern flank of the Alps and in Valais. Numerous naturally triggered medium and large avalanches are to be expected. Exposed parts of transportation routes may be at risk. The danger is also expected to increase to level 4 in northern and central Grisons as the day progresses. The danger in this region will initially mainly affect alpine snow sports terrain.
On Tuesday, the avalanche danger will increase further with more snowfall within the current danger level 4 (high). Danger level 4 conditions will also be widespread across the remaining areas of Grisons. In Valais and on the northern Alpine ridge, very large avalanches are to be expected, which will reach down into the valleys along the usual avalanche paths and endanger exposed parts of transportation routes. In the affected areas of Grisons, many medium and large avalanches are expected due to the weak but thin Snow deposited on the ground in a multiplicity of layers.EAWS glossary.