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Avalanche Forecast

Archived

Dec 10th, 2022–Dec 11th, 2022

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Kootenay Boundary, Bonnington, Grohman, Kootenay Pass, Norns, Rossland, Ymir, Kokanee, Retallack, Valhalla.

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.

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.

Problems

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.