Regions
Kootenay Boundary.
There is uncertainty in how incoming snowfall with interact with recent wind slabs and deeper weak layers. Treat avalanche hazard as Considerable if over 25 cm new snow accumulates.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Tuesday
Weather Forecast
MONDAY NIGHT: Cloudy with scattered flurries, up to 5 cm accumulation. Alpine temperatures near -15C. Ridgetop winds moderate from the south-southeast.TUESDAY: Flurries, 7-15 cm accumulation with up to 20 cm accumulating near Kootenay Pass and the US border. Alpine temperatures near -8C. Ridgetop winds moderate gusting strong from the southwest.WEDNESDAY: Mix of sun and cloud. Alpine temperatures near -8C. Ridgetop winds moderate decreasing to light from the east-southeast.THURSDAY: Cloudy with scattered flurries, trace to 5 cm accumulation. Alpine temperatures near -8C. Ridgetop winds light from the southeast.
Avalanche Summary
Several large (size 1-2.5) natural wind slab avalanches occurred on all aspects at treeline and above sometime late Friday evening into Saturday. Widespread wind effect was noted through the weekend with scouring and wind-loading on a variety of aspects. Small (size 1-1.5) wind slabs were reactive to skier traffic.
Snowpack Summary
A dusting of new snow fell on a collection of wind-affected surfaces found at all elevations: scoured and wind-pressed surfaces in alpine and exposed areas with hard wind slabs in lee features, to softer wind slabs and loose, dry snow at at lower elevations and in sheltered terrain. This wind-affected snow overlies a variety of snow surfaces: sun crust on southerly aspects to mountain top, variable wind-affect and wind-press in north to westerly terrain, and weak feathery surface hoar crystals down 20- 40 cm in sheltered areas at treeline and below . The snowpack now hosts two buried surface hoar layers. The one that was buried on February 1st (down 20-40 cm) seems to be more predominant and reactive to human triggers than the one buried deeper down (40-80 cm). This deeper layer of surface hoar may be most reactive below treeline on shady aspects but doesn't seem to be a widespread problem in the region. The mid-pack is generally well-settled and strong.
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.