Regions
Kootenay Boundary.
Large amounts of recent storm snow may push the hazard higher than forecast. Choose your riding terrain carefully and be conservative with route selection.
Confidence
High - Due to the number and quality of field observations
Weather Forecast
A Pacific frontal system is forecast to pass through the region later today with light precipitation overnight and through Monday.Upper elevations may see 5 cm of new snow. There should be a bit of a break Monday evening, then a weak system on Tuesday will bring clouds, but very little precipitation is forecast. A ridge of high pressure will rebuild over the province bringing clear skies and no precipitation through the remainder of the week. Freezing levels will rise to 1000 metres during the day, then drop to valley bottom overnight.
Avalanche Summary
Numerous skier controlled, explosive controlled and naturally triggered storm slab avalanches were reported yesterday and ranged up to size 3. Early reports today list 3 skier accidentals in the region. These most likely failed in response to heavy storm and wind loading throughout the past week.. A number of these avalanches released on the February crust interface mentioned in the Snowpack Discussion section. The combination of wind, rapid loading, warm temperatures and increased radiation on solar aspects makes for a perfect recipe for large avalanches.
Snowpack Summary
Parts of the region received another 10 to 20cm of snow overnight. Light winds that accompanied the recent snowfall may transport the new snow into lee terrain and hide previously wind loaded pockets. 90-120 cm below the surface a hard melt-freeze crust exists that formed during the 2nd week of February. This crust is quite widespread and may co-exist with weak surface hoar or facets. This variably reactive interface is a critical layer to watch in the region and has caught a few people by surprise in recent days. Buried surface hoar layers exist in the top 120 cm in drier areas on the west side of the region near Rossland. In other areas a January surface hoar layer can be found 100-190 cm deep and poses a low probability/ high consequence threat. It should remain on your radar, especially in thin snowpack areas and during periods of significant warming or rapid loading.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.