Regions
Kootenay Boundary.
Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain on Saturday
Weather Forecast
Saturday: 10-15cm of snow - Moderate to strong southwest winds - Freezing level at 1000mSunday: Some ridging in the morning with trace amounts of snow forecast for the afternoon - Light southwest winds - Freezing level trending from surface to 600m throughout the dayMonday: Light snowfall - Light to moderate west winds - Freezing level at 600m
Avalanche Summary
Ski-cut sluffs to size 1.5 were observed throughout the region on thursday. A few skier-accidental slabs to size 1.5 (30-50 cm crowns) were also observed in the Nelson area. Expect a spike in avalanche activity with Friday night/Saturday's forecast weather.
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 friday night's forecast heavy snow, strong winds and rising freezing levels will add a new load to any buried weaknesses, and create a reactive "upside-down" snow pack.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
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.
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.