Regions
Banff Yoho Kootenay.
The first big storm of the winter is beginning now, along with the first avalanche cycle of the winter for Thursday and Friday. Ice climbers should stay away from avalanche gullies, and skiers be aware that the snowpack is weak and unstable. GS
Weather Forecast
A significant storm embedded in a westerly flow will cross the regions with periods of snow starting Wednesday evening, depositing 50-60 cm by Friday morning. Treeline temperatures will range from -5 to -10 with moderate SW winds, gusting to strong. Following this storm, skies will clear and temperatures will plummet to -30 on Saturday.
Snowpack Summary
A weak and almost entirely facetted snowpack exists across the forecast region at this time. With the arrival of the current storm starting on Wednesday night, upwards of 50-60 cm additional snow could fall by Friday. This will most certainly overload the weak base, and slab avalanches are expected at treeline and above.
Avalanche Summary
No new avalanche observed or reported today.
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.