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Avalanche Forecast

Archived

Dec 30th, 2022–Dec 31st, 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.

Human-triggered avalanches are likely wherever a slab sits over the deeper facet layers. This is not a problem you can outsmart, and the ways to reduce risk are through avoidance of avalanche terrain or choosing slopes where the consequences of an avalanche will be smaller.

Confidence

High

Avalanche Summary

Avalanche control over the last few days has produced large avalanches up to size 3 in many different areas. Some were initiated on the Dec. 17 interface but most stepped down to the basal facets. Lake Louise ski hill triggered numerous slides with explosives today, including a size 3 in Boundary Bowl. It slid on the basal facets and produced debris up to 3.5m deep. Visitor Safety Specialists remote-triggered a size 2.5 from a ridge on Mt. Simpson Thursday, and there was also a skier-triggered incident on Bow Peak which luckily just resulted in lost gear. Flights today and yesterday observed a natural cycle that occurred sometime in the past week up to size 2.5.

Snowpack Summary

Slabs 25-60cm sit atop a weak layer of facets and surface hoar (Dec. 17th interface). Below this, the snowpack is generally facetted with the weakest facets and depth hoar near the bottom. Snowpack depths at treeline range from 80-150cm throughout the region.

Weather Summary

Some light snow overnight into Saturday AM with up to 5cm overnight in the Little Yoho area, and less to the East. On Saturday expect a few cm with most in Little Yoho, 30-40km/h West ridgetop winds, and valley bottom freezing levels. Flurries will die off Saturday night, with winds shifting to West-Northwest in the 30-40 km/h range at ridgetop.

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.