Regions
Banff Yoho Kootenay.
Wind and storm slabs in the alpine continue to react to skier traffic today. The potential for heating keeps treeline hazard ratings at moderate over the next few days.
Weather Forecast
Clear skies will lead to a solid freeze overnight Sunday. Despite the potential for flurries Monday, freezing levels are still forecast to reach 2200m as unsettled air tracks east from the coast: don't rule out loose wet activity and light rain BTL. Tuesday should see West winds return to the moderate range with the potential for flurries.
Snowpack Summary
Sunday morning saw 5 to 10cm storm snow over recent crusts below 2300m. Solar heating is making new crusts today. 20-50cm of snow over the last week in the alpine sits over crusts on S aspects and was redistributed by moderate west winds. At tree line and above the mid-pack is a 120cm+ firm slab overlying weaker basal facets in much of the region.
Avalanche Summary
Skiers triggered a sz 2 slab at 2500m on the S aspect of Mt Jimmy Simpson 40 deep over a crust on a 30 degree slope. A field team on the Wapta reported sz 2 windslabs: 1 on the SE aspect of Mt Ayesha, and 2 on the East aspect of Arete Peak, an icefall triggered sz 2 slab off of the East aspect of Mt. Collie, and sz 1.5 loose wet off the S of Gordon
Confidence
Timing, track, or intensity of incoming weather system is uncertain on Monday
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
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.