Bulletin d’avalanche

Snowdrifts, weak layering, increasingly frequent glide-snow avalanches

Snowdrifts, weak layering, increasingly frequent glide-snow avalanches

Fresh snow and drifts are increasingly prone to triggering with ascending altitude, can release even with minimum additional loading. Avalanche prone locations are found particularly above 1800 m, in steep ridgeline terrain and in wind-loaded gullies and bowls. Activities beyond secured ski slopes require experience in avalanche assessment on-site and defensive conduct in awareness of risks. In addition, at high altitude shady steep terrain, weak ground level layers can trigger in transltion zones from deep to shallow snow by large additional loading in particular. If avalanches fracture down to deeper layers of the snowpack they can grow to large size. Exposed zones can be placed at risk. At low and intermediate altitudes on steep grass-covered slopes, in forest clearances and on hillsides, increasingly frequent naturally triggered glide-snow avalanches are possible. Glide cracks in the snowpack are red flags. Exposed zones can be placed at risk. Below about 2000 m on sunny slopes, moreover, superficial, wet loose snow avalanches can trigger naturally.

Above 1700-1900 m there was an insignificant amount of new snow. The snow, particularly in exposed high-altitude ridgeline zones, was transported by intermittently strong-velocity winds. Fresh snow and drifts become increasingly prone to triggering with ascending altitude. Through the markedly higher temperatures the new snow and snowdrifts of last week are settling. They lie atop loose, sometimes bonded snow of an increasingly consolidated snowpack. Bonding inside the upper layers, often riddled with graupel, and to the old snowpack is moderate to poor, making it prone to triggering. At mid-level of the snowpack on high-altitude shady slopes, faceted crystals are evident. Below 1800 m the old snowpack is well settled, but moist. There is currently only limited data available from high altitude zones.

Rainfall, above 1900 m snowfall, will pass through this morning but clouds and residual fog disperse only slowly. Subsequently, sunshine will emerge in the high alpine regions. It is mild for this juncture of the season: zero-degree level at 2100-2500 m. Temperature at 2000 m: -1 to +3 degrees. Moderate northerly winds at high altitude.

The danger of dry-snow avalanches will gradually decrease. Due to strikingly higher temperatures the danger of wet avalanches will increase during the course of each day. In addition, glide-snow avalanches continue to be expected.