Regions
Banff Yoho Kootenay.
Although just over the peak of the avalanche cycle, we continue to see large avalanches running. The CONSIDERABLE danger rating below treeline exists due to the potential to be hit from above. Avalanches have been running to the valley bottom.
Weather Forecast
Southwest flow continues with flurries expected on Wednesday night, possible accumulations of 3-5 cm by Thursday. The temperatures will fall slightly on Thursday, but expect freezing levels to reach about 1500 meters and treeline temperature from -5 to -8. Winds will remain moderate from the southwest.
Snowpack Summary
100cm of dense, rounded snow comprises the upper half of the snowpack and sits on a very weak base of depth hoar. This unstable structure produces consistent, sudden collapse test results in the depth hoar layer approximately 60cm from ground. Two shears persist near the surface down 15 and 35cm indicating lingering instability in the storm snow.
Avalanche Summary
Report of big avalanche activity on the Bow Hut approach today. Fresh size 2 avalanche over the trail, and a very large (estimated size 3.5) deep slab from the Vulture Glacier ran over the Bow Hut headwall and covered the trail through the moraines. These are our only reports from today, but they indicate that large avalanches remain very likely.
Problems
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.
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.