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 - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
The first of two weekend weather systems is expected to reach the interior on Friday. Thursday may see light scattered flurries and freezing levels should be around 1000m with light to moderate alpine winds from the SW. The Purcells region can expect 3-6mm on Friday with freezing levels around 1000m and moderate alpine winds from the SW. On Saturday freezing levels will rise to around 1500m and alpine winds are expected to be moderate from the west. Light scattered precipitation is expected on Saturday. The models currently have the second storm system reaching the interior early Sunday.
Avalanche Summary
No new avalanches have been reported since Monday. On Monday, explosive control produced a size 3 deep slab avalanche and a snowmobile triggered a size 1.5 wind slab. On Sunday, a report of a skier remotely triggering a size 2.5 avalanche from 5 meters away in the Dogtooth range alpine. This occurred at around 2300m in the alpine. Also reported was an explosive triggered size 2 persistent slab releasing around 60cm deep.
Snowpack Summary
A surface crust exists up to around 2200 m. Above this elevation is dry storm snow which is settling out and faceting. A new layer of large 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. Tests are suggesting that this layer is getting difficult to trigger but still has the potential to produce large avalanches. 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.