Regions
Kootenay Boundary.
Many parts of the region will reach the tipping point with forecast new snow and wind for Tuesday. Large, easily triggered avalanches are very likely.
Confidence
Poor - Intensity of incoming weather is uncertain
Weather Forecast
Tuesday: A Pacific frontal system arrives bringing 10-15 cm new snow and strong westerly winds, which at ridge top could reach 100 km/h. Freezing levels will spike to around 1500 m in the afternoon. Wednesday: the cold front associated with the system moves through, bringing further moderate amounts of snow and bringing freezing levels down to around 1000 m. Winds should become moderate northwesterly. Thursday: Dry, with light northwesterly winds and freezing levels around 800 m.
Avalanche Summary
Numerous size 1 and 2 avalanches have been reported from this region, running on a variety of aspects and elevations and with crowns up to 40 cm deep.
Snowpack Summary
Snowfall Sunday night added a further 10-20 cm, bringing the amount of snow that now lies above the early February weak layer to around 40 cm. This is right at the critical depth where triggering is very likely and resulting avalanches could easily be large enough to bury a person. The early February weak layer comprises large surface hoar on sheltered aspects, facets on northerly aspects and a crust on solar aspects--professionals are treating this layer with extreme caution, since it is showing signs of remote triggering and the ability to propagate in low angled terrain. Alpine winds have been strong enough to blow snow around, adding touchy wind to the problem, especially behind exposed terrain features in the alpine. In shallow snowpack areas concerns remain for the mid-December persistent weakness down around 80-100cm and for basal facets. Treeline snowpack depths are approximately 230 cm.
Problems
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
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.