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 places. Avalanches may be triggered mainly at transitions from a shallow to a deep Snow deposited on the ground in a multiplicity of layers.EAWS glossary and can still become very large.
- 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 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 in these layers are less frequent and the main danger comes from the new and drifted snow. Ridgelines and ridges were often cleared by the northwesterly wind. Below approximately 1800 m, the Snow deposited on the ground in a multiplicity of layers.EAWS glossary has been soaked by the sometimes intense 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 Friday
A little snow fell in the north above 1000 m during the night. It was quite sunny in all regions in the late morning, but clouds moved in again from the west in the afternoon.
Fresh snow
From Thursday afternoon to Friday morning above 1400 m:
- Westernmost Lower Valais, northern Alpine ridge from Les Diablerets to the Jungfrau region: 20 to 30 cm
- Jura, rest of Lower Valais, rest of northern Alpine ridge, northern Grisons: 10 to 20 cm
- Elsewhere less, dry along the central southern flank of the Alps
In total, the following amounts of snow have fallen above 2200 m since the onset of precipitation on Tuesday:
- Westernmost Lower Valais, northern Lower Valais: 100 to 140 cm
- Vaud Alps and Fribourg Alps, the rest of Lower Valais, the rest of the northern Alpine ridge west of the Grimsel Pass: 60 to 80 cm
- Remaining western and central parts of the northern flank of the Alps, western Ticino, southern Upper Valais: 30 to 60 cm
- Eastern part of the northern flank of the Alps, northern Grisons, rest of Ticino: 20 to 40 cm, less elsewhere
Temperature
At midday at 2000 m, around -2 °C
Wind
- Strong to storm force from the northwest during the night
- During the day moderate to strong in the west at high altitudes, otherwise light to moderate from the southwest
Weather forecast to Saturday
On Saturday, it will be very cloudy and there will be some precipitation at times; in the south, this will occur during the night, while in the north it will be during the day. The snowfall level in the south will be around 1200 m, while in the north it will drop down to low altitudes.
Fresh snow
From Friday to Saturday evening above 1400 m:
- Simplon area, western Ticino: 5 to 10 cm
- Elsewhere a widespread few centimetres
Temperature
At midday at 2000 m, between -4 °C in the north and -1 °C in the south.
Wind
- Moderate to strong southerly wind during the night, which will then ease and change into a northerly wind
- Increasingly moderate from the northeast during the day
Outlook
Sunday
On Sunday there will be some more precipitation in the north with sunny spells in the afternoon. Conditions will be quite sunny in the south. There will be a strong northerly wind overnight to Sunday along the Main Alpine Ridge and south of it.
The avalanche danger will continue to decrease in the west, but will not change significantly in the other regions. The northerly winds will lead to the formation of snowdrift accumulations, which will be prone to triggering.
Monday
Overnight to Monday, the precipitation will intensify from the west and two days of heavy snowfall will begin. On the northern flank of the Alps and in Valais, 40 to 60 cm of fresh snow is expected to fall by the evening. The snowfall level will rise temporarily to 1400 m overnight to Monday and fall to low altitudes during the day. The westerly wind will be frequently strong to storm force.
The avalanche danger will increase to high (level 4) in the north on Monday. Naturally triggered avalanches are expected to increase as the day progresses.