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Avalanche Forecast

Archived

Dec 29th, 2022–Dec 30th, 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

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

The deeper weak layers are active and human-triggered avalanches are likely. A special avalanche warning has been issued which includes our region.

Avalanche control will be conducted on Mounts Stephen, Field, and Dennis in Yoho on Dec. 30, 2022. These areas are closed to any activities during this time. Click here for maps of the closure zones.

Confidence

Moderate

Avalanche Summary

Avalanche control over the last couple of days has produced large avalanches up to size 3. These were on Mt. Bourgeau along the Sunshine Village Access Road, Mount Whymper, and Simpson. Some were initiated on the Dec. 17 interface, with many stepping down to the basal facets. Visitor Safety Specialists remote-triggered a size 2 from a ridge on Mt. Simpson, and there was also a skier-triggered incident on Bow Peak which luckily just resulted in lost gear. A natural cycle over the last 24-48 hours up to size 2.5 was observed on a flight along the range.

Snowpack Summary

Slabs sit atop a weak layer of facets and surface hoar (Dec. 17th interface). Below this, the snowpack is generally facetted with the largest facets and depth hoar near the bottom. Snowpack depths at treeline range from 80-150cm throughout the region.

Weather Summary

On Friday, increasing clouds with minimal accumulations and West ridgetop winds 20-40km/h. Freezing levels will remain at valley bottom. On Friday evening, another wave from the Pacific will bring snow to the region, with 5cm forecast for places such as Little Yoho.

Terrain and Travel Advice

  • Uncertainty is best managed through conservative terrain choices at this time.

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.

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.