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Avalanche Forecast

Archived

Dec 12th, 2021–Dec 13th, 2021

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

Regions

Banff Yoho Kootenay.

The bulk of the stormy weather has passed but unsettled conditions will remain with us for a few days. While we expect natural activity has dropped off, the potential for human triggering will linger. 

Weather Forecast

Winds have backed off to the moderate range and remain out of the SW Sunday evening and may diminish a bit further into Monday before returning to moderate into Tuesday. Temperatures have cooled to -10 Cat treeline and should remain there through Tuesday as a few cm of snow trickles in. 

Snowpack Summary

Up to 30 cm of storm snow since Saturday. 25-45 cm of snow now overlays the Dec 2 crust which is present up to 2100-2250 m. At treeline and above, strong to extreme W & SW winds have developed slabs in lee areas with extensive wind effect in exposed areas. The weak Nov 5 crust/facet interface is present near the ground.

Avalanche Summary

In the past 36 hrs there have been a few reports of skier triggered slabs at treeline including ski patrol and MIN reports. Additionally, explosive work at the ski hills produced several other slabs Beyond this there have been a few reports of natural avalanches generated out of the alpine described as audibles or visible as powder clouds.

Confidence

Due to the quality of field observations on Sunday

Problems

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

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.

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.