Appenzeller Alpen

Especially on wind-protected shady slopes, fresh and drifted snow from the last period of precipitation is lying on an old snow surface which is faceted in many places, or on surface hoarTransparent, 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. The connection to the old snow surface is therefore poor in many places. Deeper layers of the snowpackSnow deposited on the ground in a multiplicity of layers.EAWS glossary are mostly well consolidated in northern Lower Valais and on the northern flank of the Alps. South of a line from the Rhône to the Rhine, the entire snowpack is often faceted and loose. In these regions, avalanches can start deeper in the snowpack. WhumpfingDistinctive 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 remote triggering, including over relatively large distances, are still being reported. The probability of slab avalanchesThe abrupt release of a slab of snow on a mountain slope. After crack initiation and crack propagation in a weak layer the released slab comprises 3 elements: The weak layer, the gliding horizon and the slab. If the slope angle is steep enough, the slab will glide down. If the slope is not steep enough, the slab will settle down on the failed weak layer. Possibly a whumpf sound will follow due to air pressed out of the weak layer. The fracture line will be sharp edged.EAWS glossary being triggered is decreasing only slowly and will require patience. Dangerously large avalanches can still be easily triggered by human activity, especially on the northern flank of the Alps, in Valais and in northern Grisons.

With the mild weather, the snow is becoming wet at low and intermediate altitudes. Fresh snowdrift accumulations at high altitude are mostly small.

On Tuesday, conditions were initially overcast, then increasingly sunny from the west.

Fresh snow

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Temperature

At midday at 2000 m, between +4°C in the north and -2°C in the south

Wind

Mostly moderate from westerly directions

On Wednesday, conditions will be mostly sunny in the north, with sunny intervals in the south.

Fresh snow

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Temperature

At midday at 2000 m, between +2°C in the north and -2°C in the south

Wind

• in the north: moderate southwesterly, occasionally strong in the Jura and at high altitudes
• in the south: mostly light southwesterly

Thursday

In the north, conditions will rapidly become sunny after an overcast night. Cloud cover will be very heavy in the south. There will be a moderate southwesterly wind.

Avalanche risk will decrease, but only slowly due to the weak snowpackSnow deposited on the ground in a multiplicity of layers.EAWS glossary structure.

Friday

Conditions will be mostly sunny in the north and overcast with light precipitation in the south. The snowfall level will be around 1200 m. The night to Friday will see a strong southwesterly wind at high altitudes and in the regions that are exposed to the foehn wind in the north; otherwise winds will be mostly moderate.

With the foehn wind, easily triggerable snowdrift accumulations will develop in the north. Deeper layers of snow will stabilise only slowly due to the weak old snowpackSnow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary, especially in areas south of a line from the Rhône to the Rhine. Avalanche risk may increase slightly on the southern flank of the Alps with any fresh snowfall.