Regions
Kootenay Boundary.
Treeline hazard may be higher near Rossland where buried surface hoar has been more reactive.
Confidence
Moderate - Freezing levels are uncertain
Weather Forecast
No significant snow or wind in the forecast. The big news is BIG warm up on Tuesday with a temperature inversion and freezing levels possibly rising to near 3000m near Kootenay Pass and 2000m further north in region.
Avalanche Summary
A skier triggered size 1.5 persistent slab avalanche was reported in the Rossland area on Friday. It was at 1700m on an east aspect and failed on a layer of buried surface hoar down approximately 35cm in a cut block.
Snowpack Summary
15-20cm of recent storm snow with moderate to strong southwest winds have created wind slabs that are stubborn, but still possible to human trigger. In isolated locations where winds were the strongest there may be hard slabs that can propagate long distances if triggered. This new snow lies above a variable old surface buried at the end of January. This interface is being reported as a layer of surface hoar at treeline in the Rossland area. However, in most other parts of the region the new snow sits on a rain crust and/or old wind slabs. A weak layer of buried mid January can be found down 45-50cm and seems to be gaining strength. Deeper in the snowpack, the surface hoar layer that was buried earlier in January is now down 80-120 cm and continues to give isolated sudden planar fractures in snowpack tests under heavy loads.
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.
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.