Monthey-Val d'Illiez

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 bonding 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 relatively well consolidated in the extreme west of 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 release deeper in the snowpack.

On Sunday, many avalanches, some large in the west, were triggered by human activity, some remotely over relatively long distances. 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 were very prevalent. The probability of triggering 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 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.

During the night to Monday and on Monday morning, some regions in the north saw a little precipitation. The snowfall level rose to 1600 m. Otherwise, it was mostly cloudy in the north. There were sunny intervals in the inneralpine regions and conditions were mostly sunny in the south.

Fresh snow

-

Temperature

Rising markedly, reaching between 0°C in the west and north and -4°C in the south at midday at 2000 m

Wind

During the night to Monday the westerly wind freshened and once again became moderate to strong.

On Tuesday, conditions will be very sunny in the north and mostly cloudy in the south.

Fresh snow

-

Temperature

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

Wind

Southwesterly:

• sometimes strong overnight at high altitudes on the northern flank of the Alps, otherwise moderate
• strong at times in the Jura
• foehn in the north

On Wednesday, conditions will again be mostly sunny in the north at first, becoming increasingly cloudy in the afternoon. The southwesterly wind will freshen up again at high altitudes and in the Jura. There will be some rain, especially in the Jura, until Thursday morning. Thursday will be quite sunny. Conditions will be very cloudy in the south on both days.

The risk of dry avalanches will decrease further, but only very slowly in the areas south of a line from the Rhône to the Rhine 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. Avalanche risk will not change significantly on the southern flank of the Alps.