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Archived

Avalanche Forecast

Dec 12th, 2021–Dec 13th, 2021
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

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

Avalanche Problems

Loose Dry

20 to 30 cm of storm snow has developed ideal conditions for loose dry avalanches in steep terrain, including below treeline where the new snow sits on the slippery Dec 2 crust. Human triggered activity will remain likely until the new snow settles.

  • Be careful of loose dry sluffing in steep, confined or exposed terrain.
  • If triggered dry loose point releases can form deeper deposits in terrain traps.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 1.5

Wind Slabs

Strong winds and new snow Friday though Saturday created fresh wind slabs in exposed terrain at treeline and above, and extensive wind effect in open areas. Human triggering of these slabs will remain likely in steep wind loaded terrain on Monday.

  • Watch for shooting cracks or stiffer feeling snow. Avoid areas that appear wind loaded.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 2.5

Deep Persistent Slabs

The new snow load may increase the likelihood of avalanches on the Nov 5 crust/basal facets for a few days. Steep shallow snowpack areas, cross loaded rocky terrain and areas exposed to large triggers such as cornices are the most concerning.

  • Be aware of the potential for full depth avalanches due to deeply buried weak layers.
  • Avoid steep convexities or areas with a thin or variable snowpack.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 2 - 3