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Avalanche Forecast

Archived

Dec 11th, 2022–Dec 12th, 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.

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.

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.