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Archived

Avalanche Forecast

Dec 7th, 2019–Dec 8th, 2019
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.

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

Avalanche Problems

Storm Slabs

30-50 cm of recent snow accompanied by strong SW winds have formed a storm slab in many open areas at treeline and in the alpine. Human triggering of this slab will remain likely on Sunday though natural avalanche activity will slow down.

  • If triggered the storm slabs may step down to deeper layers resulting in large avalanches.
  • Use caution in the alpine and treeline. Storm snow is forming reactive slabs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1.5 - 2.5

Deep Persistent Slabs

The snowpack structure under the new snow is weak, consisting of facets and depth hoar. If an avalanche is triggered it has potential to scrub down to these deeper layers resulting in larger avalanches.

  • Watch for whumpfing, hollow sounds, and shooting cracks.
  • Be aware of thin areas that may propogate to deeper instabilites.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 1.5 - 3