Avalanche Forecast
Regions: Bonnington, Grohman, Kokanee, Kootenay Boundary, Kootenay Pass, Norns, Retallack, Rossland, Valhalla, Ymir.
Large avalanches reported on Friday indicate the buried weak layers are primed for human triggering, particularly at treeline elevations.
Continue to make conservative terrain choices and reduce your exposure to avalanche terrain. Stick to simple terrain, free from overhead hazards.
Confidence
Moderate
Avalanche Summary
On Friday activity was reported on the persistent weak layers buried mid November, as new snow added load to the snowpack. Numerous remotely triggered avalanches (from up to 100 m away) were reported throughout this region, up to size 2. These avalanches either failed on the November weak layers or 'stepped down' from a smaller avalanches onto these deeper instabilities. Activity was reported on all aspects, from 1800-2300 mostly in sparsely treed terrain. Persistent slab avalanches were also triggered by explosives on this layer, 70-100 cm deep.
Control work also produced slab avalanches within the storm snow up to size 2, around 40 cm deep. We expect conditons to remain sensitive to human triggers.
Snowpack Summary
Steady snowfall has delivered around 40 cm over the last 3 days. Southerly winds will have redistributed new snow into wind loaded features at higher elevations. This new snow sits over a small layer of surface hoar in sheltered and shaded terrain and a sun crust on sunny south facing slopes.
A concerning layer of large and weak surface hoar crystals, facets and a melt freeze crust sits 50-80 cm deep, buried in mid November. This layer has been very reactive at treeline between 1700-2200 m, on all aspects producing large remotely triggered avalanches. This layer could become more reactive with new snow, wind and rising temperatures.
Snowpack depths average 80-160 cm in the alpine.
Weather Summary
Saturday Night
Cloudy with up to 6-12 cm of new snow. Moderate southwest winds. Freezing level below valley bottom.
Sunday
Mostly cloudy with isolated flurries bringing up to 5 cm amounts of new snow in the morning, cloud begins to clear in the afternoon. Freezing levels rise to 900 m in the afternoon, alpine high of -2. Light northeast winds.
Monday
Partly cloudy. Light northeast winds. Freezing level below valley bottom, alpine high of-6.
Tuesday
A mix of sun and cloud. Light northeast winds. Freezing level below valley bottom. Alpine high -8.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
- Continue to make conservative terrain choices while the storm snow settles and stabilizes.
- Don't let the desire for deep powder pull you into high consequence terrain.
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
Avalanche Problems
Persistent Slabs
A weak layer of surface hoar and facets from mid November is buried down 50 to 80cm in the region. In the last 3 days large and surprising remotely triggered avalanches have occurred on this layer. As new snowfall continues to add load to the snow pack it is likely that this layer will become more sensitive to triggering.
Use extra caution at treeline where this layer is more prominent and look for signs of instability like shooting cracks, whumpfing and recent avalanches.
Be aware that small avalanches within the recent storm snow may trigger larger avalanches on these deeper instabilities. Read our newest blog to learn more about this concerning layer and how to manage it.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible - Likely
Expected Size: 1.5 - 2.5
Storm Slabs
Expect storm snow to remain reactive to human triggers on Sunday. Watch for wind loaded slopes at higher elevations, on north and east facing terrain.
Don't forget that storm slabs could step down to deeper layers resulting in larger and more destructive avalanches.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 2