Regions
Kootenay Boundary.
Good terrain selection becomes a more subtle art as stability improves. Choosing supported terrain and avoiding wind loaded areas will help you to hedge against uncertainty in the snowpack.
Weather Forecast
Thursday: A mix of sun and cloud. Winds light from the north. Freezing level around 800 metres with alpine temperatures around -8. Friday: Mainly cloudy with isolated flurries bringing a trace of new snow. Winds light from the southwest. Freezing level to 700 metres with alpine temperatures around -9. Saturday: Cloudy with sunny periods and isolated flurries beginning in the evening. Winds moderate from the west. Freezing level to 700 metres with alpine temperatures of -9.
Avalanche Summary
Reports from Tuesday reveal a continuation of Monday's avalanche activity, with a skier-triggered Size 2 storm slab occurring on a southwest aspect south of Nelson, as well as numerous explosives controlled storm slabs ranging from Size 1.5-2 running on north and northwest aspects. Crown depths have averaged around 20 cm, but have also been noted as deep as 50 cm. Monday's reports included four natural Size 1.5 storm slabs observed in the Kootenay Pass area at 10-20 cm thick. Ski cutting and explosives control resulted in numerous storm slabs Size 1-1.5 throughout the region. These slabs were 10-30 cm thick and were failing on all aspects above around 1800 m elevation. For Thursday, expect our storm slab problem to remain in the realm of human-triggering. Storm slabs may fail on a storm interface or could release a bit deeper on the widespread crust layer. Deeper instabilities in the snowpack also remain an isolated concern, meaning that storm slab avalanches have the potential to step down to deeper layers and result in very large avalanches.
Snowpack Summary
At higher elevations, 30-50 cm of recent snow overlies a series of crust layers from mid-February. Recent reports suggest this snow is generally well bonded to the crust. On high north aspects, a layer of surface hoar from mid-February may sit below the recent snow and may still be reactive. In exposed terrain, recent southerly winds have scoured the new snow down to the crust and formed wind slabs in leeward features. The early-February surface hoar layer is now down approximately 80-100 cm. This layer was reactive during the warm storm last week but now appears to have gone dormant. Areas with a shallow snowpack (less than around 150 cm) generally have a weak snowpack structure with a layer of sugary facets near the ground.
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.