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Avalanche Forecast

Archived

Dec 9th, 2022–Dec 10th, 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 unlikely, human triggered possible.
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.

Use conservative terrain selection in any area displaying a slab of cohesive snow in the upper snowpack. This season's low snow inputs and cool temperatures have favored a weak lower snowpack.

Early season hazards remain poorly covered.

Confidence

Moderate

Avalanche Summary

A report of a few sz 1.5 slabs initiating in the alpine lees on Mt Dennis and scrubbing to the ground came in Friday afternoon. Lake Louise reported 14/15 shots producing results in untouched terrain, several of which were persistent slabs to sz 2. Sunshine village remote triggered some very soft slabs on the walls of the Canyon BTL.

Snowpack Summary

Snow inputs have continued for the past 4 days amounting to 10-40cm with up to 20cm last night at Sunshine. This, combined with previous moderate SW winds has formed wind slabs at higher elevations. These slabs have contributed the persistent slabs that sit on a weak base made up of facets, surface hoar and a crust. Average snowpack depths at treeline are 60 to 100 cm throughout the region.

Weather Summary

Following a brief ridge overnight with alpine temps -15to -20C , a frontal system off of the coast will push moderate SW winds carrying flurries into the area Saturday morning. Alpine temps -5 to -10C during the day and -10 to -15C overnight.

Terrain and Travel Advice

  • Uncertainty is best managed through conservative terrain choices at this time.
  • Approach lee and cross-loaded slopes with caution.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger 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.

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.