Regions
Kootenay Boundary.
Warm temperatures and sunshine on Thursday should maintain touchy conditions. Conservative terrain selection is still crucial at this time.
Confidence
Fair - The weather pattern is stable
Weather Forecast
Synopsis: A strong ridge of high pressure will maintain dry, sunny, and mild conditions for Thursday. An above freezing layer (AFL) is likely between 1500 and 2500 m. Ridge top winds should be light or moderate from the NW. On Friday the AFL should shrink and we might start seeing increasing cloud throughout the day. Theres a chance of flurries on Saturday as the freezing level drops back to valley bottom.
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. There were also reports of skiers and machines triggering slab avalanche from a distance (remotely and sympathetically triggered).
Snowpack Summary
30 - 60 cm of snow fell across the region earlier this week with moderate southwest winds shifting these accumulations into deeper deposits in lee terrain. Warm temperatures may keep the storm storm slab sensitive to light triggers. The new 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. Up to 100 cm below the surface, 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.