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Avalanche Forecast

Archived

Dec 12th, 2022–Dec 13th, 2022

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

Conservative terrain selection is essential to manage the deep persistent slab problem.

Use caution on any steep slopes where a cohesive slab is found.

The consequences of getting caught are high right now with thin snowpack values providing poor coverage for rocks and logs.

Confidence

Moderate

Avalanche Summary

Following explosive control efforts on Saturday, SSV snow safety triggered a sz 2.5 slab at 2300m on a NW aspect 40 to 130cm deep and 50-60m wide running 240m on the basal facets. Further explosive control work produced an additional sz 2 deep persistent slab 40m wide at 2700m on a NW aspect. A sz 2 windslab off of Crowfoot Mountain on a NE aspect at 3000m was reported to have run 700m and over the ice climb located near the toe of the glacier

Snowpack Summary

20-60 cm of snow has formed a soft slab over a very weak base consisting of facets. Thin crusts can be found on the facet interface at lower elevations and on solar slopes. Recent moderate southwest winds have formed slabs at higher elevations. Snowpack depths at treeline range between 60 and 120 cm.

Weather Summary

A ridge has formed over British Columbia with a Pacific low pressure system currently swinging north of the ridge into northern Alberta.

Very light north winds bringing colder alpine temperatures (-15- to-20C) can be expected overnight Monday before the low starts its descent through the prairies Tuesday. Moderate to strong northerly winds, some light snowfall and alpine high temperatures near -10C can be expected Tuesday afternoon.

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.