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Avalanche Forecast

Archived

Dec 7th, 2019–Dec 8th, 2019

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 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.

The avalanche hazard will remain elevated on Sunday though natural avalanche activity will taper off. Make conservative terrain choices for skiing and climbing and avoid exposure to steep slopes and terrain traps.

Weather Forecast

Another 5-10 cm of snow is expected Saturday night in the Banff area. Winds will gradually start tapering off as a cooler air system moves in on Sunday and the weather clears. Expect an alpine high of -8'C to -12'C on Sunday with a mix of sun and cloud and light to moderate ridge top winds from the NW.

Snowpack Summary

30-50+ cm of snow has fallen since Tuesday with moderate to strong SW winds. A storm slab has formed at treeline and above. Below the storm slab, the snowpack structure is generally weak, consisting of facets and depth hoar. The Nov crust exists up to 2400m and 30 cm up from ground. Snowpack depths at treeline are 80-130 cm and deeper in lee areas.

Avalanche Summary

Numerous avalanches have been observed and reported up to size 2.5 over the last 72 hours, including at least two skier triggered size 2's in the Lake Louise backcountry. These have primarily been storm slabs in the new snow though some have scrubbed down into the facets. Explosive control at the local ski areas has produced results up to Sz 2.5.

Confidence

Forecast snowfall amounts are uncertain on Sunday

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.