Regions
Kootenay Boundary.
Lingering storm slabs have become difficult to trigger but may still be reactive in recently wind loaded terrain or high north facing slopes where buried surface hoar may be lingering.
Confidence
Moderate - Intensity of incoming weather systems is uncertain on Tuesday
Weather Forecast
Lingering flurries are expected Sunday overnight and Monday during the day totaling around 5 cm. Alpine wind is forecast to be moderate from the southwest and afternoon freezing levels are expected to reach around 1400 m. On Tuesday, a low pressure system reaches the region and 15-20 cm of new snow is expected be Tuesday evening. Alpine wind is forecast to be strong from the southwest and afternoon freezing levels are expected to reach around 1500 m. Light snowfall is forecast to continue Tuesday overnight and Wednesday morning with another 5-10 cm currently expected. Sunny breaks are forecast for Wednesday afternoon with light alpine wind and afternoon freezing levels around 1000 m.
Avalanche Summary
No new avalanches were reported on Saturday. On Friday, natural activity was limited to one size 1.5 storm slab avalanche on a north aspect and numerous loose wet avalanches up to size 2.5 from south aspects. Explosives and ski cutting triggered numerous storm slabs up to size 2 on north aspects above 2000 m with 10-40 cm thick slabs. On Thursday, a natural size 3 persistent slab avalanche was observed on a northeast aspect at 2100 m elevation. The slab was 200 cm thick and was suspected to have failed on an old facet layer in the middle of the snowpack. Widespread natural avalanche activity occurred during the storm on Thursday including storm slabs up to size 3, mainly from north facing alpine terrain. The recent storm snow has generally stabilized but may still be reactive on north aspects where buried surface hoar is preserved, steep slopes where the crust acts as a sliding layer, or recent wind loaded terrain features. Deeper weak layers have become difficult to trigger but smaller avalanches could still step down and result in very large avalanches in isolated areas.
Snowpack Summary
At higher elevations, 30-40 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 below the recent snow 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 interface is now down approximately 80-100 cm. This interface comprises a variety of surfaces, including scoured surfaces in wind exposed terrain, surface hoar (size 2-3 mm) in sheltered locations, and sun crust on steep solar aspects. This layer is still reactive to snowpack tests but is becoming difficult to trigger. Areas with a shallow snowpack (less than around 150 cm) generally have a weak snowpack structure with sugary facets near the ground. This includes shallow alpine slopes and most of the Rossland range. In these areas it is possible for storm slab avalanches to step-down to these deeper weak layers, resulting in large avalanches.
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.