Avalanche Forecast
Regions: Bonnington, Kootenay Boundary, Kootenay Pass, Moyie, Norns, Rossland, South Okanagan, St. Mary, Ymir.
Watch for pockets of wind slab at upper elevations from recent northerly winds. These slabs may be in atypical areas due to reverse-loading and are particularly reactive on southern aspects where they overlie a crust.
Confidence
Moderate
Avalanche Summary
On Saturday, explosives control produced wind slab avalanches to size 2 on southern aspects. Several size 1 wind slab avalanches, triggered by skier traffic, were reported throughout the region. A few size 1 natural loose dry avalanches were observed in steep terrain.
Avalanches on the persistent and deep persistent weak layers have not been reported within this region recently. However, operators further north in the Selkirks continue to report natural and human-triggered avalanches on these buried weak layers.
Snowpack Summary
10-20 cm of snow is being redistributed by moderate northerly winds into deep pockets at the alpine and treeline. On southerly aspects, snow sits above a melt-freeze crust while on northerly aspects it overlies previously wind-affected surfaces.
Several weak layers are found mid-snowpack. The primary concern is the early January surface hoar (40-80 cm deep). Observations suggest that this layer is rounding and beginning to bond but may still be reactive in sheltered and shaded terrain features.
A thick melt freeze crust from Boxing Day is buried 70-100 cm deep. This layer is helping to cap lower snowpack weaknesses but is a concern at higher elevations where this crust is thin and less supportive.
The lower snowpack contains weak and facetted grains. Concern remains for heavy loads to trigger this layer such as cornice falls, machine triggers or step down avalanches. Check out the latest forecaster blog on these deep weak layers here.
Weather Summary
Sunday Night
Clear skies. Moderate northerly ridgetop winds occasionally gusting 60 km/h. Alpine low temperatures of -20°C.
Monday
Sunny with increasing afternoon cloud. Moderate northerly winds switch to westerly in the afternoon. Alpine high of -12°C.
Tuesday
A mix of sun and cloud with isolated flurries, trace accumulation. Westerley ridgetop winds 40 km/h. Alpine high of -10°C.
Wednesday
A mix of sun and cloud with isolated flurries, trace accumulation. Trace accumulations of snowfall. Light westerly ridgetop winds occasionally gusting 40 km/h. Alpine high of -7°C.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
- Wind slabs may be poorly bonded to the underlying crust.
- In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
Avalanche Problems
Wind Slabs
On Saturday we received several reports of small wind slabs that were reactive to skier traffic on southerly aspects. Moderate northerly winds continue to build reactive wind slabs over a crust in alpine lees.
Recent winds have varied throughout the region - look for wind affected snow on all aspects as you approach or descend from ridgelines. In sheltered terrain wind loading potentially sits over buried surface hoar, propagation may be wider than you expect.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 2
Persistent Slabs
A persistent weak layer of surface hoar is buried 50 to 70 cm down. This depth is prime for human triggering. Buried surface hoar is more likely to be preserved in terrain features protected from wind and sun effect.
The lower snowpack is comprised of weak, faceted grains and can be triggered under the right circumstances. Be especially suspicious of shallow, rocky, or cross-loaded areas with variable snow depths.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Unlikely - Possible
Expected Size: 2 - 3.5