Regions
Banff Yoho Kootenay.
We cautiously drop the treeline danger rating to Moderate, but expect that human triggered avalanches remain likely in many areas at treeline and above. Don't let the lack of natural avalanche activity fool you. Travel carefully.
Weather Forecast
The westerly flow continues with no snow in the forecast until early Thursday morning. Treeline temperatures on Wednesday will range from -4 to -8 with alpine winds increasing to 50-70 km/hr by the afternoon. A total of 5 cm of snow is expected by Friday.
Snowpack Summary
The snowpack remains fundamentally weak, with a combination of windslab, surface hoar and basal facets all causing concern in different types of terrain. Snowpack tests continue to produce moderate, sudden results on the Dec 18 layer down 40 cm from the surface. Human triggering is likely.
Avalanche Summary
No natural avalanches observed, but human and explosive triggered avalanches persist. Yesterday someone in the Sunshine Village backcountry triggered a windslab that took them for a 50m ride. Avalanche control on Mt Dennis in Field today produced no slabs, but loose snow avalanches ran 1000m over Pilsner Pillar.
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
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.