Churfirsten and Rhine Valley
Appenzeller Alpen
Hard-to-read day. Considerable, with wind slab and persistent weak layers in play — you can read the surface problem; the buried one sets the consequence.
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
Over the last few days there has been heavy snowfall in the north, which in particular at the start was transported by strong to storm-force winds. In the south, the sometimes storm-force northerly wind has primarily transported loose old snow.
On shady slopes sheltered from the wind in particular, the fresh and drifted snow is overlying 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 and also buried 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 the upper part of the Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary. Saturday saw avalanches triggered in these weak layers by winter sports participants. In the inneralpine regions of Valais and especially Grisons, the Snow deposited on the ground in a multiplicity of layers.EAWS glossary remains weak, and there is a possibility of isolated avalanches releasing even in near-ground weak layers.
With fresh snow and wind, further mostly small snowdrift accumulations will form on Sunday in the north.
Weather review for Saturday
The day started off sunny, but clouds gathered from the west in the afternoon, with the first snowflakes falling in the Jura.
Fresh snow
-
Temperature
At midday at 2000 m, between -4 °C in the north and +1 °C in the south
Wind
Moderate northerly, strong at times on the main Alpine ridge
Weather forecast to Sunday
Snow will fall overnight down to low altitudes. Only the south will remain dry. During the day, conditions will remain very cloudy in the north, with a little snow continuing to fall primarily in the northeast. Conditions will be mostly sunny in Valais and the south.
Fresh snow
- Northern flank of the Alps: 10 to 20 cm, in the central Prealps up to 30 cm
- less elsewhere; dry in the south
Temperature
At midday at 2000 m, between -8 °C in the north and -4 °C in the south
Wind
- Moderate north to northeasterly, strong at times at high altitudes
- Strong Bise wind in the western Prealps and the Jura
- Strong foehn wind in the south
Outlook to Tuesday
After a calmer spell overnight, an increasingly strong northwesterly wind will set in on Monday. On Monday evening, the wind will veer to the north and will reach storm-force at times at high altitudes and in the south. On Monday morning there will be light snowfall at first, which will become heavy down to low altitudes from midday onwards. By Tuesday afternoon, 50 to 70 cm of snow will have fallen on the northern Alpine ridge and in northern Prättigau, with a widespread 20 to 40 cm elsewhere. In the far south, both days will be comparatively dry and sunny.
Avalanche danger will not change significantly in the south, but in all other areas it will increase from midday on Monday. In the north, increasing numbers of naturally triggered avalanches are to be expected, with danger level 4 (high) possibly being reached in places over the course of Tuesday.