Regions
Banff Yoho Kootenay.
New wind slabs will remain easy to trigger for the next day or so until the winds ease and the new snow has a chance to bond. Sunday and Monday should allow for good travel and ski conditions but pay attention to daytime heating as the skies clear.
Weather Forecast
Moderate to strong west winds with light snowfall will continue through Saturday night before easing up on Sunday morning. Freezing levels will creep higher Sunday and higher still Monday with increasing solar influence as a ridge and clearing skies arrives on Sunday afternoon.
Snowpack Summary
5cm of new snow over a melt freeze crust on all aspects at tree line, and up to 2900m on solar aspects. 20-50cm of snow over the last week in the alpine with moderate west winds creating soft slabs and rapid cornice growth. At tree line and above the mid-pack is a 120cm+ firm slab overlying weaker basal facets in much of the region.
Avalanche Summary
Reports of a couple skier triggered wind slabs in the alpine at Bow Summit and Cathedral Peak on Friday as the winds increased. Propagation up to 100m was reported. On Saturday local ski areas were seeing rapid cornice growth and were able to ski cut small wind slabs in lee areas throughout the day. No new naturals observed but visibility was poor.
Confidence
Timing of incoming weather systems is uncertain on Tuesday
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.