Stoos

Sunday's layers of new and drifted snow are becoming increasingly stable. The number of places where avalanches can be triggered in these layers is decreasing. Western Ticino and the western and central parts of the northern Alpine ridge have seen the largest volumes of new and drifted snow. The probability of triggering in buried 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, which is primarily present in southern Valais and in Grisons, is also decreasing.

Isolated avalanches are repeatedly being triggered in near-ground 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 inneralpine regions and southern parts of Grisons. These avalanches may still become large. In other regions, although there are still weak layers in the near-ground old snowpackSnow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary on shady slopes, they are mostly so thickly covered that they are very unlikely to be triggered.

With warming and solar radiation on Tuesday, there may be loose snow slides originating from near-surface snow layers, especially in rocky terrain.

Overnight to Monday and during the day there was a little snowfall, especially in the north above 1400 m. There were sunny spells in the west and south, but cloud cover was heavier towards the east.

New snow

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Temperature

At midday at 2000 m, between -3 °C in the north and 0 °C in the south

Wind

Northerly:

• moderate at times on the northern Alpine ridge and on the main Alpine ridge
• elsewhere light

After a mostly clear night, conditions will mainly be sunny during the day.

New snow

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Temperature

Rising, reaching around 0 °C at midday at 2000 m

Wind

Mostly light from northerly directions

After a partly clear night into Wednesday, cloud cover will increase from the west in the morning. Conditions will initially remain mostly sunny, especially in the east and south. Later on, cloud cover will increase there as well while, in the north, precipitation will set in over the course of the afternoon. By the evening, 10 to 20 cm of snow will have fallen on the northern flank of the Alps; elsewhere less. The snowfall level will rapidly drop from 1200 m to low altitudes by the evening. Winds will rise appreciably in the morning, becoming strong to storm force in the north and west, while in the south and in Grisons they will be moderate to strong from westerly directions at high altitudes.

On Thursday, there will be widespread snowfall down to low altitudes in the north, and this will be persistent in Lower Valais and on the northern flank of the Alps where 30 to 50 cm of snow will fall above 2000 m; elsewhere less. There will be a storm-force northwesterly wind in the mountains. In the far south, conditions will be dry with sunny intervals in a strong northerly foehn wind.

Avalanche danger will increase, markedly so in the north over the course of the day from Wednesday onwards.