Grimselpass

Increase in avalanche danger as a consequence of new snow and wind, especially in the west.

Avalanches can be released in the old snowpack and reach dangerously large size. Whumpfing sounds can indicate the danger. Remotely triggered avalanches are possible. As a consequence of new snow and a gathering strong westerly wind, avalanche prone wind slabs will form. Backcountry touring and other off-piste activities call for experience in the assessment of avalanche danger and caution.

Snowpack At intermediate and low altitudes there is very little snow or none at all. Even above 2500 m, the snow depths tend to be below average, in the Valais snow depths are average. At 2500 m in the northern Valais, in the western Lower Valais, in Bedretto Valley and in the upper valleys of Maggia there is 80 to 120 cm of snow, in the remaining regions of Switzerland 50 to 80 cm of snow on the ground over widespread areas, and in central Grisons and the Engadine, 30 to 50 cm. The snow cover below approximatelyy 2400 m shows pronounced effects of the higher temperatures and rainfall. At elevated altitudes and in particular in high alpine regions the snowpack manifests heavy wind impact. In areas below 2200 to 2400 m there are more deeply embedded inside the snowpack expansively metamorphosed (faceted) and soft layers evident, particularly in the Valais, in the Gotthard region, in Ticino and in Grisons. These weak layers are being blanketed by varyingly thick, bonded layers. In the Valais, in northern Ticino and in Grisons, avalanches have released during the last few days which were triggered by persons and unleashed from these soft, weak layers. As a consequence of the fresh fallen snow and increasing westerly winds, fresh snowdrift accumulations will be generated, particularly on Friday in the western regions. The fresh fallen snow and freshly generated snowdrift accumulations were deposited particularly on wind-protected shady slopes on top of the loose old snowpack surface and they are highly prone to triggering. Observed weather review Thursday, 29.12.2022 On the northern flank of the Alps and in the central sector of the southern flank of the Alps, skies were predominantly overcast. During the course of the day, light precipitation set in from the northwest. The snowfall level lay at 1600 m. In the inneralpine regions it was partly sunny. Fresh snow By Thursday afternoon in the western regions, only a few centimetres from place to place. Temperature At midday at 2000 m, between 0 °C in the northern regions and -3 °C in the southern regions. Wind Winds were southwesterly:

• in the northern regions blowing at moderate to strong velocity;
• in the southern regions blowing at light to moderate strength.

Weather forecast through Friday, 30.12.2022 On Thursday night in the western and the northern regions more than anywhere else, precipitation is anticipated, above approximately 1400 m it will fall as snow. During the daytime hours on Friday, skies will be predominantly overcast and it will temporarily remain dry. Bright intervals are expected particularly in the inneralpine regions, as well as in the east and in the south. In the Engadine it will be partly sunny. During the afternoon, precipitation will set in from the west once again and the snowfall level will ascend swiftly to 2200 m. Fresh snow Between Thursday evening and Friday afternoon, the following amounts of fresh snow are anticipated above 2200 m:

• northern and furthermost western part of Lower Valais, Vaud Alps: 15 to 30 cm; on the French border as much as 40 cm;
• western sector of the northern flank of the Alps, central sector of the northern flank of the Alps west of the Reuss, remaining parts of Lower Valais, northern Upper Valais: 10 to 15 cm;
• northern flank of the Alps east of the Reuss: 5 to 10 cm; in the remaining regions of Switzerland, less; or else it will remain dry.

Temperature At midday at 2000 m, between +2 °C in the northern regions and -2 °C in the southern regions. Wind Winds will be westerly to southwesterly:

• on Thursday night at elevated altitudes blowing at moderate strength from southwesterly directions;
• during the course of the day in the northern regions, winds will intensify and, starting at midday, be blowing at strong to storm-velocity, in the southern regions blowing at moderate strength at high altitudes.

Outlook through Sunday, 01.01.2023 Saturday During Friday night in the western and the northern regions, a small additional amount of precipitation is anticipated, above 2300 m falling as snow. During the daytime on Saturday it will be predominantly sunny accompanied by high-altitude cloudbanks. As a consequence of strong-velocity westerly to southwesterly winds, it will be very mild in the mountains. The zero-degree level will ascend to 3200 m. The danger of dry-snow avalanches is not expected to change significantly at high altitudes. During the course of the day, moist slides can be expected to release from the fresh fallen snow on steep sunny slopes. Gliding avalanches are possible, particularly in the western and the northern regions. Sunday On Sunday it will be predominantly sunny, accompanied by cloudbanks. In the central sector of the southern flank of the Alps the cloud cover will be heavier and only isolated bright intervals are expected. It will remain windy and very mild. The danger of dry-snow avalanches is expected to incrementally decrease. During the course of the day, moist slides and gliding avalanches are possible on steep sunny slopes.