Bernese Oberland
Lenk
Avalanche Problems
New snow + Persistent weak layers
3=
Field notes
New snow
Easy to spot - the snow is fresh. Look at recent avalanche activity in similar terrain, and pay attention to how much new snow has fallen in the last three days. Critical loading depends on temperature, wind, and what was on the surface before the storm. SLF advises waiting until the Snow deposited on the ground in a multiplicity of layers.EAWS glossary has had time to bond before committing to steep terrain in fresh snow.
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
At the end of the past week, fresh snow fell at low temperatures. Much of this snow is still loose or has been transported by the moderate to strong Bise wind. The fresh and drift snow expected to fall during the upcoming precipitation spell will be deposited on the still cold and often loose snow during the milder temperatures on Monday and can easily be triggered as avalanche. Deeper in the Snow deposited on the ground in a multiplicity of layers.EAWS glossary, 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 that are prone to triggering, especially on shady slopes above approximately 2400 m and generally in the Areas above approximately 3000 m (particularly glaciated areas).EAWS glossary. Avalanches may also be triggered in these deeper layers in places.
Weather review for Sunday
It was already cloudy in the early morning in the west, but still sunny in the south and east. It later clouded over in these regions too.
Fresh snow
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Temperature
At midday at 2000 m, around -4 °C
Wind
- Still mostly moderate from the north during the night
- There was a moderate to strong westerly to southwesterly wind during the day in the west and on the northern flank of the Alps, and a light to moderate northwesterly wind in the south and in Grisons
Weather forecast to Monday
Precipitation from the west will set in overnight to Monday. Widespread precipitation will fall during the day, which will be persistent and intense in the west. The snowfall level will be between 1200 and 1400 m.
Fresh snow
Until Monday afternoon, the following amounts will fall above approximately 1600 m:
- Extreme west of Lower Valais on the border with France: 50 to 80 cm
- Vaud and Fribourg Alps, western Bernese Oberland, rest of northern Valais: 30 to 50 cm
- Other parts of the Lower Valais, Goms, northern flank of the Alps: 15 to 30 cm
- Otherwise less and often dry, especially in central Grisons
Temperature
In the middle of the day at 2000 m, between -1 °C in the west and north and -3 °C in the south
Wind
- In the west and on the northern flank of the Alps: strong west to southwesterly winds
- Otherwise moderate to strong southwesterly winds at high altitudes
- In the alpine valleys in the central and eastern parts of the northern flank of the Alps: moderate foehn wind in the late morning
Outlook
Tuesday
Further snowfall is expected below 1000 m, with persistent snowfall in the extreme west of Lower Valais and on the northern flank of the Alps. Another 30 to 50 cm is expected in the west, and a widespread 15 to 30 cm on the northern flank of the Alps. There will be a moderate to strong westerly wind initially. As the day progresses, the wind will shift to the northwest. It will become appreciably colder again in the north.
The avalanche danger will continue to increase, especially in the west and north.
Wednesday
In the north, snow will continue to fall to below 1000 m, mostly from the eastern Bernese Oberland to the Alpstein region, where 15 to 30 cm is expected. Some brighter spells are possible in inneralpine regions. On the southern flank of the Alps, it will be mostly sunny, with sometimes strong northerly winds extending down to the valleys.
The avalanche danger will gradually decrease in the west. Elsewhere, it will not change significantly.