Regions
Kootenay Boundary.
Danger ratings are based on 20-25cm snow accumulation and very strong winds on Tuesday. It could be slightly lower if the system is a little less intense than forecast.
Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain
Weather Forecast
A frontal system will spread light to locally moderate snowfall tonight and through Tuesday. Some areas could see up to 20cm. Winds are expected to be strong from the southwest. Wednesday should be another unsettled convective day with generally 3-5cm and lighter winds. Another system should spread light or moderate snowfall on Thursday, but the track of this system is still a little uncertain. The daytime freezing level should hover around 1000m each day.
Avalanche Summary
One recent Size 3 avalanche was observed in the north end of the region last weekend. This avalanche was suspected to have released on the early February surface hoar layer. There was also a report of a Size 2 avalanche remotely triggered by a snowcat in rocky and variable terrain on a north aspect. This avalanche occurred just outside the region to the north. Otherwise avalanche activity has been limited to Size 1 skier triggered wind slabs or loose snow sluffs.
Snowpack Summary
An additional 20cm of new snow brings the total storm snow amount to around 100cm in most areas. Several resistant shears have been noted in the storm snow. A sun crust on southern aspects and a spotty 2-6mm surface hoar on north and east aspects is down around 60-90cm. Below that, the more significant early February surface hoar is down 100-160cm. Snowpack tests show moderate to hard forces generating sudden planar shears on this layer. A melt-freeze crust, down 20-30cm, below 1800m provides some bridging to the layers below. Below the early February surface hoar layer, the snowpack is strong in most places. Cornices are very large 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.