Regions
Kootenay Boundary.
Touchy avalanche conditions are expected for the next few days. Buried weak layers exist, and can surprise with nasty consequences.
Confidence
Fair - Intensity of incoming weather systems is uncertain on Wednesday
Weather Forecast
On Monday a dry upper ridge will bring mainly sunny skies, light northwest winds and freezing levels at about 1000m. On Tuesday expect increased cloud and light snowfall as a pacific system moves eastward into the region. Snowfall will intensify on Tuesday night and Wednesday. With this system we can expect up to 30cm of snow, moderate westerly winds and freezing levels at about 1000m.
Avalanche Summary
Widespread natural and remotely triggered storm slab avalanches to size 2.5 were reported from the Rossland Range on Sunday. They occurred on a variety of aspects and elevations. The recently buried crust/surface hoar interface was the culprit in these avalanches. In one event, a remotely triggered storm slab in motion stepped down to the November crust/facet interface near the ground on a planar slope at 2100m.Looking forward, I would expect natural storm slab activity to taper-off. However, human triggered large avalanches will remain a real concern for some time to come.
Snowpack Summary
Up to 50cm of recent storm snow has been shifted by strong winds into much deeper deposits in exposed terrain. This new snow overlies a prominent surface hoar layer above a thick rain crust that extends as high as 2400 m. This crust/surface hoar interface is now reactive, as widespread whumpfing and cracking were reported from the Rossland Range. High elevation north aspect slopes do not have the rain crust, but are still reported to have buried touchy surface hoar. On these slopes, deeper facets or buried surface hoar from earlier in the month may also be lurking. At the base of the snowpack, a crust/facet combo has become less likely to trigger, although a recent avalanche indicates this destructive layer should still on our radar on steep, smooth terrain at treeline and in the alpine.
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.