Avalanche Forecast
Regions: Bonnington, Grohman, Kokanee, Kootenay Boundary, Kootenay Pass, Norns, Retallack, Rossland, Valhalla, Ymir.
The buried weak layer continues to be reactive to natural and human triggering, particularly at treeline elevation.
Watch for signs of instability whumpfing, hollow sound, shooting cracks and recent avalanche.
Confidence
Moderate
Avalanche Summary
On Saturday a skier accidental avalanche, size 2, was reported in the White Water backcountry. The avalanche released on the mid-November persistent weak layer and had a crown 100 cm deep.
Numerous remotely triggered avalanches (from up to 100 m away) were reported throughout this region, up to size 2, this weekend. 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.
On Sunday explosives control triggered numerous slab avalanches to size 2 in recent storm snow.
Snowpack Summary
Moderate southerly ridgetop winds have redistributed 30 - 40 cm of storm snow into deep pockets at higher elevations. At treeline and below new snow overlies 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
Sunday Night
Mainly cloudy with isolated flurries, trace accumulation. Light northerly ridge winds. Alpine temperatures, low of -6. Freezing levels drop from 1200 m to valley bottom overnight.
Monday
Cloudy with sunny periods. Isolated flurries, trace accumulation. Light northerly ridge winds. Alpine temperatures, high of -6. Freezing levels 1000m.
Tuesday
Mix of sun and cloud with isolated flurries, trace accumulation. Light to moderate easterly ridge winds. A weak alpine inversion brings alpine temperatures around -4 while the valley bottom remains -10.
Wednesday
Mix of sun and cloud with isolated flurries. Light to moderate northerly ridge winds. Alpine temperatures, high of -5.
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. Through the weekend large and surprising remotely triggered avalanches have occurred on this layer.
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
Expected Size: 1.5 - 2.5
Storm Slabs
With warmer temperatures on Sunday 30 -40 cm of storm, snow has become more cohesive and is reactive to human triggering. Watch for wind-loaded slopes at higher elevations, on north and east-facing terrain where slabs will be thicker.
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: Likely
Expected Size: 1 - 2