Regions
Kootenay Boundary.
More heavy precipitation in the forecast is keeping avalanche danger high.
Confidence
Fair - Forecast snowfall amounts are uncertain
Weather Forecast
Wednesday night and Thursday: Another wave associated with the frontal system should bring some good precipitation quantities (10-20 mm until Thursday evening) and with strong W winds easing off a bit Thursday but staying in the moderate to strong speeds. Freezing levels rising to 2000 m.Friday: Precipitation should start tapering off as the westerly flow weakens. Temperatures and freezing level are expected to lower (down to 1400m.). Winds should to remain in the moderate to strong from the W. Saturday: Some light precipitation is expected but not as significant as before. Light SW winds and freezing levels staying at a similar height as Friday.
Avalanche Summary
There was numerous reports of sluffing in the new snow in steep terrain and natural slab avalanches up to size 1.5 on all aspects. There was also several skier triggered slab avalanches up to size 2 also on all aspects. I suspect more and bigger natural activity today and tomorrow.
Snowpack Summary
The warm storm has already added a significant load onto the snowpack (around 30 mm of water equivalent). Another pulse of precipitation will add weight onto the storm slab and the already moist/wet snowpack below the freezing line (around 2000 m.). In the alpine and at treeline, the new snow will sit on hard wind slabs lee of NW-SW winds in alpine and treeline features, a well developed surface hoar in shaded areas above 1700 m., a melt-freeze crust below that elevation and a 3 cm sun crust on solar aspects at all elevations. At lower elevations, the wet precipitation will keep soaking up the snowpack possibly weakening it especially where there is a good buried sliding surface like a crust or a surface hoar layer. The surface hoar layer buried down 100 cm is still a concern and would generate a very large avalanche if triggered.
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.
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.