Regions
Kootenay Boundary.
Danger ratings could be a notch higher is there is prolonged sunshine on Monday.
Confidence
Fair - Forecast snowfall amounts are uncertain
Weather Forecast
Monday: Unsettled conditions with flurries or periods of snow, and possible sunny breaks (2-5cm). The freezing level should be around 1000-1200m. Winds will be moderate and gusty from the SW. Tuesday: Light to moderate snow - 5-15cm. The freezing level is around 1000m during the day and valley bottom overnight. Winds are moderate to strong from the SW. Wednesday: Unsettled conditions with cloudy skies and light flurries. The freezing level is around 800-1000m. Winds ease to light from the SW.
Avalanche Summary
Recent avalanche activity includes one Size 2 accidentally triggered avalanche. It occurred in relatively well-supported treed terrain on a north aspect. The skier triggered the avalanche in a shallow rocky area. There was also a report of a Size 3.5 avalanche on Saturday that was remotely triggered by a snowcat. This occurred just north of the region in the southern Purcells. It highlights the potential for triggered very large and destructive avalanches. Other observations on Saturday include several loose snow avalanches up to Size 2 on all aspects and skier controlled or explosive controlled avalanches up to Size 2 with 10-150cm deep crowns.
Snowpack Summary
Rain fell to around 2000 m on Thursday afternoon and froze into a crust on all aspects below this elevation. 10-30cm of new snow now sits above the crust. The previous storm snow overlies a sun crust on southern aspects and maybe a spotty 2-6mm surface hoar on north and east aspects, down around 60cm. Below that, the more significant early February surface hoar is down 80-140cm. Snowpack tests show moderate to hard forces generating sudden planar shears on this layer. Below the early February surface hoar layer, the snowpack is strong in most places. Cornices are growing and would act as a significant trigger for all the layers mentioned above if they drop.
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.
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.