Snowpack

Strong to storm force wind from westerly directions will transport fresh and old snow. At elevated altitudes, in particular on west, north and east facing slopes, the fresh snow and wind slab layers are lying on a weakly bonded old snowpack consisting of faceted snow crystals or surface hoar, and they are prone to triggering. On south facing slopes the surface of the snowpack has been influenced by the sun, and in all aspects at intermediate altitudes by rain in some instances. In these places the bonding between the snowpack and the new layers is therefore more favourable.
As a consequence of rain up to approximately 2000 m, wet snow and gliding avalanches are possible. This applies in particular on north facing slopes.
Weak layers exist near the base of the snowpack in particular on west, north and east facing slopes above approximately 2200 to 2400 m, and on south facing slopes above approximately 2800 m. From central Valais through Ticino to Grisons, in some places these layers can still be released by people. In the extreme west of Lower Valais and on the northern flank of the Alps, the weak layers are embedded so deep that they are now very unlikely to be released by people.

Observed weather on Monday, 27.12.2021

Sunday night was mostly clear, except in Ticino. During the day the east remained quite sunny in the morning, otherwise it was mostly cloudy. As the day progressed, light precipitation commenced in the west and south. The snowfall level was approximately 1300 to 1500 m.

Fresh snow

Elevated altitudes in the western Jura: 5 to 10 cm
Elevated altitudes in the eastern Jura, Prealps, extreme west of Lower Valais, Ticino: a few centimetres

Temperature

At midday at 2000 m: about 0 °C in the north and -3 °C in the south

Wind

On Sunday night over a wide area and in the south during the day as well, light to moderate from the southwest
In the north during the day, moderate, in the regions exposed to the foehn wind and in the Jura, moderate to strong from the southwest

Weather forecast through Tuesday, 28.12.2021

Monday night will be partly bright at first, before precipitation arrives from the west during the second half of the night. During the day it will be mostly cloudy and precipitation will fall over a wide area. In Ticino the skies will clear during the day, and it will be partly sunny in the afternoon. In the morning the snowfall level will rise to approximately 1800 to 2000 m in the west and the Prealps. Otherwise it will be 1400 to 1600 m.

Fresh snow

From Monday afternoon until Tuesday afternoon the following amounts of snow will fall above approximately 2000 m:

Northern flank of the Alps from Chablais into the Muota valley, Lower Valais: 15 to 30 cm, but as much as 40 cm in the extreme west of Lower Valais
Upper Valais, rest of the Gotthard region, eastern part of the northern flank of the Alps, Prättigau: 10 to 20 cm
Elsewhere: a few centimetres

Temperature

At midday at 2000 m: between +1 °C in the northwest and -1 °C in the southeast

Wind

During the night in the west and north, strong, otherwise light to moderate from the southwest to west
During the day at elevated altitudes over a wide area, strong to storm force from the west to northwest

Outlook through Thursday, 30.12.2021

Wednesday

An exceptionally warm and most air mass will reach the Swiss Alps on Wednesday. In the north and in Valais there will be heavy precipitation. The snowfall level will rise significantly, to approximately 2800 m in the west and to approximately 2500 m in the east. In the high Alpine regions in the north and Valais, 50 to 80 cm of snow is likely to fall, but smaller amounts are expected in Grisons and the south. The amounts of precipitation remain uncertain. In the far south it will be dry and mostly sunny.
The wind will be strong to storm force from the west to northwest and transport large quantities of fresh snow.
The danger of both wet snow and dry avalanches will increase significantly. In the regions north of a line between the Rhone and Rhine (excluding both the Prealps and the Jura), and in Valais, the Gotthard region, northern Grisons and northern Lower Engadine, danger level 4 (high) is likely to be reached over a wide area. The avalanche prone locations will be very widespread; as a consequence of intense rainfall, both a large number of often large wet snow avalanches and, at elevated altitudes, large to very large dry avalanches, are to be expected. In the other regions of both Grisons and Ticino, the avalanche danger will also increase, but less significantly.

Thursday

On Wednesday night the precipitation will persist over a wide area of the north and east. The snowfall level will drop to approximately 2300 m. On the northern flank of the Alps from the eastern Bernese Alps to the Alpstein region, and in northern Grisons, a further 20 to 40 cm of snow is to be expected. Smaller amounts are expected elsewhere. The south will remain dry. During the day the precipitation will cease and the skies will brighten from the west. It will be mostly sunny in the south.
The avalanche danger will decrease in the west, probably to level 3 (considerable). In the northern and eastern regions exposed to precipitation it will remain at level 4 (high) at first; it is likely to decrease later, but not until the day progresses.