Regions
Banff Yoho Kootenay.
The great conditions will continue until mid-day Thursday, but then it all changes. An avalanche cycle will be in full force by Friday with up to 40 cm expected, freezing levels to 2000m and winds exceeding 110 km/hr. Head for the trees!
Weather Forecast
The weather is changing as a strong system moves into the area embedded in a westerly flow. Expect 5-10 cm Thursday, 15-25 Friday, and 10 cm on Saturday. Significant warming and winds accompany this system, with freezing levels to 2000 m on Friday and SW wind exceeding 100 km/hr. This may not come true, as the models disagree on snowfall amounts.
Snowpack Summary
35-50 cm of recent storm snow sits on a crust from January 30, and in isolated locations (east of the divide) has been blown into windslabs. Over the next few days, as the next storm begins to add load, this bond to the Jan 30 interface will be critical. Expect windslabs by Thursday, with human triggered and natural avalanches likely by Friday.
Avalanche Summary
One natural size 2 avalanche was observed on Mt. Redoubt near Lake Louise, approximately 60 m wide and failing on the ground level depth hoar. Good backcountry observations were made from Sunshine Village and the Brewster Creek area, and no new avalanches were observed here.
Confidence
Intensity of incoming weather systems is uncertain on Friday
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.