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
This week's fresh and drifted snow is gradually settling and consolidating. 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, there are some 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 and some snow-covered 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, particularly on wind-protected shady slopes. On Saturday in particular, avalanches were 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 structure remains weak, and there is a possibility of isolated avalanches starting even in near-ground weak layers.
With light snowfall and northerly winds, mostly small snowdrift accumulations formed on Sunday, especially on the northern flank of the Alps. These will continue to grow during the course of Monday in all regions.
Weather review for Sunday
During the night, snow fell in the north down to low altitudes, mainly in the Prealps. During the day, it was mostly cloudy in the north. A few centimetres of snow fell locally. There were bright spells in Valais. In the south, conditions were very sunny.
Fresh snow
- Northern flank of the Alps: 10 to 15 cm, in the Prealps 15 to 25 cm
- less elsewhere; dry in the south
Temperature
At midday at 2000 m, around -7 °C in the north and -4 °C in the south
Wind
- Moderate to strong from north to northeast
- Moderate Bise wind in the western Prealps, sometimes strong in the Jura
- Moderate to strong foehn wind in the south
Weather forecast to Monday
It will be cloudy in the north. Light snowfall will set in on Monday morning and intensify during the course of the day. The snowfall level will be between 600 and 900 m. In the south, it will be mostly sunny after a partly clear night.
Fresh snow
- Northern flank of the Alps, Lower Valais, northern and central Grisons: 5 to 10 cm; 15 cm from the eastern Bernese Alps to the Glarus Alps
- less elsewhere; dry in the south
Temperature
At midday at 2000 m, between -6 °C in the north and -3 °C in the south
Wind
- During the night into Monday, moderate northerly winds at high altitudes
- From the northwest and increasingly strong during the day, sometimes stormy in the afternoon
- Moderate to strong foehn wind in the south
Outlook for Tuesday and Wednesday
In the north, it will be mostly very cloudy on both days and snow will fall down to low altitudes. In the south, it will be mostly sunny on both days. In Valais, it will be partly sunny on Tuesday and quite sunny on Wednesday. From Monday afternoon to Wednesday afternoon, 50 to 80 cm of snow will fall on the northern flank of the Alps from the eastern Bernese Alps to the Glarus Alps and in Grisons north of the Anterior Rhine. 30 to 50 cm will fall on the rest of the eastern part of the northern flank of the Alps and in the rest of northern and central Grisons. There will be 10 to 30 cm of snow elsewhere. It will remain largely dry south of the Main Alpine Ridge. At high altitudes, the wind will be strong to stormy from northerly directions and will transport the fresh snow as well as loose old snow. In the south, there will be a sometimes strong foehn wind. Over the course of Wednesday, the wind will ease at high altitudes and a strong Bise wind will rise in the Jura.
In the north, the avalanche danger will increase significantly during the night into Tuesday across a wide area. On Tuesday, the avalanche danger is expected to reach danger level 4 (high) in the regions exposed to heavier precipitation on the northern flank of the Alps and in northern Grisons, with naturally triggered avalanches to be increasingly expected. These may be very large on the northern flank of the Alps and exposed parts of transportation routes may be in danger. In northern Grisons, the danger will primarily affect alpine snow sports terrain. Naturally triggered avalanche activity will decrease during the course of Wednesday. However, the situation will remain very critical for snow sports outside marked and open pistes.
The avalanche danger will increase somewhat in places in the south on Tuesday, and will not change significantly on Wednesday.