Boletín de aludes

Pronounced persistent weak layers. Caution urged towards fresh snowdrifts

Pronounced persistent weak layers. Caution urged towards fresh snowdrifts

Pronounced weak layers inside the old snowpack can be triggered even by one sole skier, especially in Rätikon, Silvretta and Verwall on W/N/E-facing slopes. This applies especially to transitions from shallow to deep snow above 2000 m, e.g. entries into gullies and bowls. Also remote triggerings are possible in isolated cases. Triggered avalanches can easily grow to dangerously large size. The fresh snowdrift accumulations are often still prone to triggering. Due to fresh snow and wind, the snowdrift accumulations will continue to expand during the morning. Avalanches can be triggered by the weight of one person and reach medium size. In addition, the snowdrift accumulations formed at the beginning of the week are still prone to triggering in isolated cases on shady slopes above 1800 m. For winter sports enthusiasts the situation is critical, above all else the persistent weak layer is a threat, and very difficult to perceive/assess. A defensive route selection is important.

Last night there was a small amount of fresh snow registered in Bregenzerwald, Allgäu Alps, Arlberg and Tannberg. The snowfall will continue until midday, another 10 cm will be added to it, up to 15 cm on Arlberg and Tannberg. The fresh snow is being deposited on a snowpack surface with huge marks of sun and wind. Only in wind-protected W/N/E facing terain is the surface still powdery. Strong westerly winds are transporting the new snow, generating fresh snowdrift accumulations which are prone to triggering. Due to daytime warmth and solar radiation, the deep snowdrifts from the beginning of the week were able to settle and consolidate, particularly on sunny slopes; on shady slopes there are still prone to triggering in isolated cases. Pronounced weak layers at mid-level inside the snowpack are evident. They are prone to triggering on W/N/E-facing slopes and very difficult to evaluate. Where these layers are covered over by thick fresher layer they are no longer a threat. In Rätikon and Verwall and Silvretta, the covering is shallower, thus they can be triggered, particularly in transition zones from shallow to deep snow.

Cold front, bringing gloomy nighttime skies into the day with it, and frequent snowfall, heaviest in Bregenzerwald and Arlberg. This afternoon, conditions will quickly turn dry, the clouds disperse. Temperature at 2000 m will recede to about -9 degrees. Initially strong westerly winds, later slackening off and shifting to northwest.

Saturday will be very sunny. Sunday will have a few harmless clouds, sunshine, slight foehn influence. Avalanche danger will gradually diminish.