Regions
Banff Yoho Kootenay.
Avalanche control on Mt Bosworth (March 6,2017), no backcountry recreation in this area. A reactive storm slab has produced large avalanches through the forecast region.
Weather Forecast
Light precipe with accumulation of 3-6 cm over the next 24 hours, temperatures are expected to stay cooler through tuesday with lows of -20 and highs around -10. Forecasted winds will remain light to moderate in the alpine for tomorrow.
Snowpack Summary
20-40cm of new has fallen during the storm. This has developed a storm slab that sits over a supportive mid-pack, with the lower half of the snowpack consisting of weak facets and depth hoar. New cornice growth and isolated wind effect near ridge crest developed during the storm but has now tapered off as the winds died down .
Avalanche Summary
Natural and skier triggered avalanches to size 3 were reported today, initiating in the storm slab and in some cases stepping down to the deep persistent problem. Explosive control work on the sunshine road produced several size 2-3 avalanches. A number of remote triggered storm slabs have occurred in the last 48 hours.
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.