Bulletin d’avalanche

Caution urged towards fresh snowdrifts and weak layers

Caution urged towards fresh snowdrifts and weak layers

Southerly foehn winds are generating small, trigger-sensitive snowdrift accumulations which can be triggered even by the weight of one sole skier but generally remain small sized. Weak layers can be triggered by large additional loading, e.g. a group without distances, on W/N/E-facing slopes, particularly above 2000 m in transitions from shallow to deep snow, e.g. at entries into gullies and bowls. Triggered avalanches can grow to large size. In steep rocky terrain, small superficial loose-snow avalanches can release due to solar radiation and daytime warming. Glide-snow avalanches possible on steep grassy slopes.

The fresh snow from Friday was transported by southerly winds in Rätikon and Silvretta. Foehn wind will generate further drifts today which are prone to triggering. The new drifts were deposited frequently atop melt-freeze crusts on sunny slopes, on shady slopes atop settled powder, elsewhere above the treeline atop wind-pressed old snow: they are often prone to triggering. During the day the fresh wno on steep sunny slopes will become moist. Pronounced weak layers are evident at mid-level inside the snowpack. 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. Avalanches can fracture down to deeper layers and then grow to large size. On crests are often powerful, leaning cornices which require attentiveness.

Sunny, not-too-cold mountain weather, cloudless blue skies all day long, hardly any wind (through stronger this afternoon). Nighttime skies will be dry with little cloud. Temperature at 2000 m: -4 to -2 degrees. Moderate SW winds at high altitude.

Another day of sunshine, little wind before on Monday afternoon intensifying southerly wind brings in cloud clover. Avalanche danger will not change significantly. On Tuesday, avalanche danger will increase as a result of fresh snow and wind.