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Archived

Avalanche Forecast

Dec 11th, 2021–Dec 12th, 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
2: Moderate
The avalanche danger rating in the alpine will be moderate
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.

New snow and strong winds have increased the avalanche hazard at all elevations for Sunday.

Weather Forecast

This storm should bring another 10-15 cm overnight before moving out of the region early Sunday morning with only light flurries remaining. Temperatures will drop following the storm. Expect to see highs of -12 to -15 C at treeline on Sunday. Wind speeds will also drop into the moderate range out of the SW in most areas with some strong gusts.

Snowpack Summary

Up to 15 cm of new snow Saturday with more expected overnight. 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 open areas. The weak Nov 5 crust/facet interface is present near the ground.

Avalanche Summary

Several skier and explosive controlled wind slab avalanches up to size 2 were reported by the local ski areas along with some smaller dry loose avalanches. A few other reports of small skier triggered wind slabs and natural sluffing in steep terrain were also received.

Confidence

Timing, track, or intensity of incoming weather system is uncertain

Avalanche Problems

Loose Dry

15 to 30 cm of new snow will provide ideal conditions for loose dry avalanches in steep terrain, including below treeline where the new snow sits on the slippery Dec 2 crust. Natural activity will slow with less wind but is still possible.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 1.5

Wind Slabs

Strong winds and new snow have created fresh wind slabs in exposed terrain at treeline and above, and extensive wind effect in open areas. It will probably be fairly easy to trigger these slabs in steep wind loaded terrain on Sunday.

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

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

Elevations: Alpine, Treeline.

Likelihood: 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.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 2 - 3