A deeply buried weak layer remains a concern, especially on steep north facing slopes in the alpine. Remote triggering of this layer may still be possible.
Confidence
Fair - Due to the number and quality of field observations
Weather Forecast
The high pressure will continue to dominate for Wednesday and Thursday. On both Wednesday and Thursday, expect a mix of sun and cloud and treeline temperatures around -10C. On Friday, the high pressure begins to break down as a weak system pushes into the interior from the coast. Currently the models are not showing any substantial precipitation but it is a possibility. Alpine winds are expected to remain light from the SW for the forecast period expect possibly on Thursday night when they may increase to moderate.
Avalanche Summary
No new avalanches were reported on Monday or by publish time on Tuesday. On Sunday, snowmobiles remotely triggered a persistent slab with a crown depth around 1.5m in the Allan Creek area. On Saturday, two size 2 remotely triggered persistent slab avalanches were reported. These were triggered from 250m away and released 80-100cm down on the old rain crust from early November. These occurred around 2000-2200m elevation on NW aspects.
Snowpack Summary
A surface crust exists up to around 1800m elevation. 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. The early November crust/facet layer is down around 1 m in the south of the region, probably less in the north. We received reports that this deep weak layer has resulted in remotely triggered avalanches over the weekend.
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.