Avalanche Forecast
Regions: Bonnington, Kootenay Boundary, Kootenay Pass, Norns, Rossland, South Okanagan, Ymir.
Continually assess the snowpack for signs of instability. Be especially suspicious of shallow or rocky ridges and start zones.
Confidence
Moderate
Avalanche Summary
A widespread and reactive storm slab was reported around the region Friday and into Saturday. Skiers, vehicles, and explosives triggered slabs to size 2.5 with most crowns 30-50 cm deep, and many reported at treeline elevations 1700-2100 m (note poor visibility and no alpine observations). Most avalanches have been reported failing on the most recent interface or a crust/surface hoar layer about 10 cm lower. Wet, loose avalanches were observed in below tree line terrain.
On Saturday, explosives triggered a large (size 2.5) deep persistent slab avalanche (on the western side of the Forecast region, which has received a bit more storm snow over the weekend). This avalanche continues to indicate that while a large load was applied to this slope, this deep persistent layer is still reactive to triggers.
Please continue to share any observations or photos on the Mountain Information Network.
Snowpack Summary
Flurries continue to accumulate around the region, and another 5-15 mm is forecast overnight Sunday through Monday afternoon.
Weekend precipitation fell as rain at lower elevations with freezing levels exceeding 1900 m. Upper elevation storm snow totals vary from 15-30 cm.
At higher elevations, 20-60 cm of snow over the last week has buried a layer of surface hoar from the start of January in wind-sheltered terrain, primarily around treeline.
A facet/crust layer is down 40-90 cm (and 2-10 cm thick at TL elevation), below the mid-pack below is settled and consolidated.
A concerning and weak layer 20-50 cm facets and crust makes up the basal snowpack. Treeline snow depths average 150-210 cm.
Weather Summary
Sunday night
Cloudy with isolated flurries, up to 5 cm. Light south ridgetop wind. Treeline low temperature below -3 C. Freezing level falling below 1000 m.
Monday
Flurries through the day, up to 10 mm in 24 hours. Light to calm south-southwest ridgetop wind. Treeline high temperature 0 C. Freezing falling below 1200 m.
TuesdayMostly cloudy with very isolated flurries. Light to calm northwest ridgetop wind. Treeline high temperature -2 C.
WednesdayCloudy with isolated flurries. Increasing south ridgetop wind. Treeline high temperature -4 C.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Closely monitor how the new snow is bonding to the old surface.
- In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
Avalanche Problems
Storm Slabs
Additional flurries ridgetop wind will perpetuate the avalanche problem. Watch for more reactive pockets in open or alpine terrain. A weak layer of surface hoar is reported 30-50 cm below recent snow, possibly allowing slabs to be larger than expected. A few other concerning layers are found in the snowpack, however, recent avalanches seem to be within the storm interface or on the above-noted surface hoar.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 2
Deep Persistent Slabs
Weak, faceted grains make up the basal snowpack. Where supportive to riders, a melt-freeze crust may be providing a bridging effect, making it more difficult to trigger deeper layers. Be especially suspicious of shallow or cross-loaded areas with variable snow depths.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Unlikely
Expected Size: 2 - 3.5