Regions
Kootenay Boundary.
Watch for increasingly stormy conditions starting Friday afternoon.
Confidence
Fair - Intensity of incoming weather is uncertain on Saturday
Weather Forecast
Friday: Mostly flurries during the day with heavier snowfall starting in the afternoon. Winds will be from the west, initially light, increasing through the day. The freezing level will rise to around 1000 m. Friday night: Significant accumulations of new snow - around 20 cm. Saturday: Further snow with another 10-15 cm likely. Strong southwesterly winds. Freezing level briefly going up to 1500 m, but cooling off rapidly by Saturday night. Sunday: light snow, freezing levels around 500 m.
Avalanche Summary
Ski cutting produced size 1 loose and occasional soft slab avalanches on Wednesday with minimal propagation. Widespread sluffing to size 1 was noted on Tuesday and Wednesday in the new snow on steep terrain.
Snowpack Summary
Average treeline snow depths are nudging over the 2 m mark in this region. In the last seven days, between 40 and 80cm of cold, low density snow has fallen in this region, which has settled to create a storm slab 20-40 cm thick. Cold temperatures have kept the snow light and cohesionless in most areas, although moderate winds have started to develop wind slabs on a variety of aspects. In some areas, the strongest winds have been at valley bottom, so don't discount the possibility of finding wind slabs in unusual places, at low elevation, in generally sheltered glades, that kind of thing. A crust now lies buried around 25-45 cm below the snow surface at elevations below 1900 m. Some areas reported this crust had a layer of surface hoar on it when it was buried. Occasional reports of small soft slab avalanches that have started to come in indicate this slab is starting to be become sufficiently cohesive to produce slab avalanches. There is a blog posting on the Forecaster Blog (link on the sidebar on the left) that discusses this issue in more depth. The mid-December surface hoar/facet persistent weakness, now down 70-120 cm, remains a concern only for very heavy triggers in thin slab areas.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.
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.