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Avalanche Forecast

Archived

Dec 12th, 2022–Dec 13th, 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 possible, human triggered probable.
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.

Numerous persistent slab avalanches caught both professionals and recreationalist off guard over the last few days. Use extra caution at treeline where triggering a persistent slab is more likely.

Read our featured blog on understanding how to manage a persistent slab problem when traveling in the backcountry.

Confidence

Moderate

Avalanche Summary

On Sunday numerous surprise human-triggered persistent slab avalanches were reported between 2200 and 1700 m. The spookiest reports on this layer are of a skier remote avalanche, size 3, at Kokanee Glacier and a skier sympathetic avalanche, size 2.5 in the Kaslo region. These avalanches either failed on the November weak layers or 'stepped down' from a smaller avalanches onto these deeper instabilities.

Storm slabs continued to be reactive during explovie control to size 1.5.

Almost every report from professional and recreational backcountry users notes signs of instability: whumpfing and shooting cracks.

Snowpack Summary

With warm temperatures storm snow has settled into a 20 - 40 cm soft slab. In the alpine snow has been redistributed by southerly winds into deep pockets. At treeline and below surface slab overlies a small layer of surface hoar in sheltered and shaded terrain and a sun crust on sunny south-facing slopes.

A weak layer of large 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 will likely continue to be reactive through the week as northerly winds build wind slabs adding additional load to the weak layer.

Snowpack depths average 80-160 cm in the alpine.

Weather Summary

Monday Night

Clear skies with northerly ridge winds 20 km/hr. Alpine temperatures, low of -5. Freezing levels valley bottom.

Tuesday

Sunny with cloudy periods. Northerly ridge wind 25 - 40 km/hr. Alpine temperatures, high of -6. Freezing levels 500m.

Wednesday

A mix of sun and cloud. Northwesterly ridge winds 30 - 50 km/hr. Alpine temperatures, high of -6. Freezing levels valley bottom.

Thursday

Clear skies. Northwesterly ridge winds 40 - 60 km/hr. Alpine temperatures, high of -7. Freezing levels valley bottom.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Give the new snow several days to settle and stabilize before pushing into bigger terrain.
  • Don't let the desire for deep powder pull you into high consequence terrain.
  • Avoid lee and cross-loaded slopes at and above treeline.

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.