Natural avalanches possible, human triggered probable.
Regions
Banff Yoho Kootenay.
A major storm is starting Wednesday night. It is a good time to ski at the resorts and stay out of avalanche terrain.
Weather Forecast
A major system is heading for the forecast region starting tonight. The models have varying data but upwards of 40cm is expected throughout Thursday and Friday. The system is accompanied by warm temperatures and moderate to strong westerly winds = a perfect recipe for avalanches!
Snowpack Summary
Wind effect exists in the alpine and at treeline. Below treeline, the surface is faceted powder. This overlies the Dec. 10th layer of facets and depth hoar which is down 60-100 cm. In thin snowpack areas, the Dec. 10th layer is mixed in with the basal facets and October crust. In thicker areas, it is a distinct layer, with a stronger snowpack below
Avalanche Summary
Two skiier accidentals and a skiier remote avalanche were reported by the public in the Banff, Yoho & Kootenay forecast region yesterday. They were all size 1.5-2 and all failed in thin snowpack areas. Two were in the alpine and one was below treeline in a steep gully feature. Avalanche control on Mt Field today produced avalanches up to size 3
Confidence
Intensity of incoming weather systems is uncertain
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
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.
Loose Dry
Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.