Kandersteg

The fresh snow in the south and the snowdrift accumulations formed by the southerly winds are lying on a very weak old snowpackSnow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary 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 snowdrift accumulations are sometimes covered with fresh snow and are thus hard to identify. Avalanches can be easily triggered at the transition from fresh and drifted snow to old snow.

There are distinct weak layersSnowpack 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 in the middle and lower part of the snowpackSnow deposited on the ground in a multiplicity of layers.EAWS glossary, particularly on wind-protected shady slopes. Such places are particularly common south of a line from the Rhone to the Rhine. Medium-sized and occasionally large avalanches can still be triggered by human activity in these weak layers. The snowpack on northern and eastern slopes in central Valais, as well as in northern Grisons, is most prone to triggering and 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 isolated remote triggering are still being reported in these regions. North of a line from the Rhone to the Rhine, the deeper layers of the snowpack are somewhat less prone to triggering and hazardous zones are less common.

Snow fell overnight in the south down to low altitudes. During the day conditions remained overcast in the south, while there was broken cloud in the north and a little snow fell in the east.

Fresh snow

From Friday evening to Sunday evening, the following amounts fell above approximately 1300 m:

• Main Alpine ridge from Monte Rosa to southern Goms, western Ticino and Val Bregaglia to the Bernina Pass: 30 to 40 cm
• rest of the Main Alpine Ridge from the Gotthard region to Upper Engadine, rest of Ticino, Val Moesa: 15 to 30 cm
• Jura, rest of the Main Alpine Ridge in Valais, rest of the Engadine: 5 to 15 cm
• elsewhere less or mostly dry

Temperature

At midday at 2000 m, around -5°C

Wind

South to southwesterly

• mostly moderate during the night
• light during the day

In the north, there will be broken to heavy cloud cover with a little snow falling down to low altitudes. In the west and in the inneralpine regions there will be some quite sunny intervals over the course of the day, with moderate northerly winds on the southern flank of the Alps.

Fresh snow

• Central and eastern parts of the northern flank of the Alps as well as Prättigau and Silvretta: 5 to 10 cm
• Otherwise a widespread few centimetres

Temperature

At midday at 2000 m, between -7°C in the north and -3°C in the south

Wind

• In the north light to moderate from westerly directions
• In the south light to moderate northerly

Tuesday

On Tuesday, there will be sunny intervals at first before thicker clouds gather from the west. In the afternoon, there will be intermittent precipitation in the Jura, with the snowfall level rising to around 1500 m. Winds will become increasingly strong from the southwest, with a strong foehn wind in the north.

Small snowdrift accumulations will form locally, resulting in a slight increase in avalanche risk.

Wednesday

Precipitation will set in from the west and south overnight to Wednesday. On Wednesday, it will be mostly very cloudy with widespread rain or snow. The snowfall level will drop gradually from around 1500 m down to low altitudes. Along the Main Alpine Ridge and south of there, 15 to 30 cm of snowfall are expected. There will be a strong southerly wind overnight, which will ease during the day and veer to the north.

Fresh snow and wind will create snowdrift accumulations that are prone to triggering. There will be a widespread increase in avalanche risk.