Regions
Banff Yoho Kootenay.
Time to stay out of avalanche terrain. Weather models predict another 30-75 cm with strong winds, if this storm continues as forecasted through tomorrow the hazard will be into Extreme for Friday.
Weather Forecast
Another 30-70 cm of snow is expected before the storm ends Friday night with the greatest amounts on the Wapta. Most weather models are in agreement. The system is accompanied by warm temperatures & moderate to strong westerly winds = a perfect recipe for large avalanches stepping down into our persistent weak layers!
Snowpack Summary
25-45 cm of storm snow so far with moderate to strong WSW wind is overloading the Dec. 10th weak layer of facets and depth hoar which is down 80-120 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
Although visibility was obscured today, a wide spread natural avalanche cycle is occurring with avalanches running well into the run out zones with avalanches up to size 3.5. We expect the cycle to continue through Friday with the ongoing storm. Continued wind transport on Saturday will keep the hazard elevated.
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.