A deeply buried weak layer remains a concern, especially on steep north facing slopes in the alpine.
Weather Forecast
The high pressure will continue to dominate for Wednesday and Thursday. On Wednesday, expect a mix of sun and cloud and treeline temperatures around -6C. Thursday will be mostly cloudy with light scattered flurries possible (0-2cm). Treeline temperatures should be around -4C. On Friday, the high pressure begins to break down as a weak system pushes into the interior from the coast. Precipitation amounts are forecast to be 3-6mm and freezing levels around 500-700m elevation. Alpine winds are expected to remain light from the SW for the forecast period.
Avalanche Summary
No new avalanches were reported on Monday or by publish time on Tuesday. On Sunday, explosive control produced avalanches to size 2.5. These occurred on N-SE aspects between 2200 and 2500m elevation. Slab depth varied from 30 to 90cm. On Saturday, isolated natural activity was reported up to size 2.5 above 2400m.
Snowpack Summary
A surface crust exists to around 2100m and is generally supportive to skiers. Above this elevation is dry storm snow which is settling out and faceting. A new layer of surface hoar is currently forming on the snow surface. In exposed alpine terrain, strong southerly winds last week may have resulted in variable distribution of the surface snow and the formation of wind slabs. A thick rain crust with facets from early November is buried over 1 m down. Snowpack tests on this deep weak layers are showing improving results, but in some locations these layers are still reactive and has the potential to release large slab avalanches.
Problems
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.