Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Regions
Banff Yoho Kootenay.
A significant avalanche cycle is starting on Thursday night and will peak on Friday. Avoid avalanche terrain on Friday, and although things may improve slightly for the weekend - extreme winds will keep the avalanche danger high on Saturday.
Weather Forecast
A strong SW flow is driving moisture over the region and bringing extreme winds right through the weekend. Expect a storm total of 30 cm by Friday morning, along with winds in excess of 100 km/hr in alpine areas overnight Thursday. Temperatures are rising also, but look to remain below freezing along the Continental Divide areas through the storm.
Snowpack Summary
10cm of new snow over the past 24-hrs and another 20cm expected by Friday will be blown into deep windslabs by extreme winds from the SW on Thursday night. These new slabs overlie a fundamentally weak snowpack comprised mostly of facets and depth hoar. Snowpack tests indicate failures, and we expect action on these layers over the next 48-hrs.
Avalanche Summary
Poor visibility today, but during our field trip to Crowfoot Pass we could hear avalanches occurring in the cliffs overhead.
Confidence
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.