Regions
Kootenay Boundary.
It's important to make conservative terrain choices even though the avalanche danger is slowly decreasing. The consequences of triggering a persistent slab remain high.
Confidence
Fair - The weather pattern is stable
Weather Forecast
Synopsis: A strong ridge of high pressure should maintain dry conditions with possible valley cloud for at least the next few days. A slight temperature inversion should stick around through Saturday with mountaintop temperatures getting close to 0 degrees. A weak upper trough slides across the province on the weekend, but this might only result in a bit more mid-level cloud and a chance of flurries. By Sunday the inversion should disappear. Winds are light gusting to moderate from the W-NW throughout the period.
Avalanche Summary
Most areas reported a fairly widespread and large natural avalanche cycle on Tuesday. Many of these slides stepped down to mid-December persistent weak layer and produced avalanches up to Size 3.5. There were also reports of skiers and machines triggering slab avalanches from a distance (remotely and sympathetically triggered). Most reported avalanches occurred above 1900-2000 m from a variety of aspects.
Snowpack Summary
Warm temperatures and previous rain have probably created a surface crust on steep solar aspects and all slopes below around 1800 m. Dry powder can still be found at higher elevations. Around 30-60 cm of settling storm snow overlies a variety of old surfaces which include heavily wind-affected surfaces in exposed locations, faceted powder and buried surface hoar in sheltered terrain. Buried 80-100 cm deep, you'll likely find a touchy weak layer of surface hoar sitting on a thick rain crust. This widespread persistent weakness exists at all elevation bands, and continues to be the primary layer of concern for the region. With the recent load of storm snow, I expect this layer to remain active with the potential for large and destructive avalanches. At the base of the snowpack, a crust/facet combo appears to have gone dormant for the time being.
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.