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Avalanche Forecast

Archived

Dec 10th, 2022–Dec 11th, 2022

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

Regions

Banff Yoho Kootenay, Little Yoho, Banff, East Side 93N, Kootenay, Lake Louise, LLSA, Sunshine, West Side 93N, Field.

Natural avalanche activity has been limited, but human triggering of the slab over the basal facets is likely in many locations...keeping us in the Moderate-Considerable hazard rating. This will likely remain for some time. Conservative terrain choices are recommended.

The thin weak snowpack also means hitting buried rocks or sticks is more likely, so travel carefully.

Confidence

Moderate

Avalanche Summary

Multiple skier and explosive-triggered avalanches between size 1 and 2 have occurred at alpine and treeline elevations over the past week on all aspects. Some of these failures initiate as wind slabs and then scrub down to the basal facets, while others fail directly on the basal facets. Lots of whumpfing and cracking on the basal facets have also been observed. We expect these conditions to persist for quite a while.

Snowpack Summary

Recent snow and moderate SW winds have formed wind slabs at higher elevations. In most other areas, 20-50 cm of snow is forming a soft slab over a very weak base of facets, with occasional thin crusts at the interface. Average snowpack depths at treeline are between 60 and 90 cm.

Weather Summary

Some light flurries are expected on Sunday but no significant accumulations. Winds will be in the light range from the S-SW. Alpine temperatures will climb to -5 to -10°C before dropping to the -10 to -15°C range Sunday night.

Terrain and Travel Advice

  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
  • Uncertainty is best managed through conservative terrain choices at this time.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Problems

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.