Avalanche Forecast

Issued: Nov 19th, 2017 4:00PM

The alpine rating is high, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Wind Slabs and Persistent Slabs.

conrad janzen, Parks Canada

Banff Yoho Kootenay.

Continued snowfall with strong winds overnight will increase the danger at all elevations Monday. Plenty of reports of avalanche activity and a couple close calls over the last two days mean this is a good time to stay out of avalanche terrain.

Summary

Weather Forecast

Strong SW winds accompanied by moderate snowfall amounts should continue through Sunday night with snowfall amounts of 10-15 cm. Temperatures will remain in the -5 to -10'C range. The winds and snowfall start easing Monday morning with temperatures cooling, then remaining steady until a slight rise on Wednesday.

Snowpack Summary

Strong SW winds with 5-15cm of new snow in the last 24 hours are creating slabs in lee areas at treeline and above which are reactive to skiers. The snowpack at treeline is from 60-90 cm deep across the region. The main feature in the snowpack is a buried layer of facets now down 30 to 50 cm and sitting on the Halloween crust in areas below 2700m.

Avalanche Summary

Continued reports of natural and skier triggered avalanche activity on Sunday. Local ski hills reported easily triggered wind slabs and persistent slabs up to size 2 with ski cutting and explosives. Several reports of natural avalanches in back country areas around Bow Summit and Emerald Lake, and one avalanche incident on Mt Crowfoot.

Confidence

Intensity of incoming weather systems is uncertain on Monday

Problems

Wind Slabs

Strong SW winds are moving a great deal of snow into lee areas at treeline and above, with lots of sluffing in steep terrain. Wind slabs have formed near ridge crests with slabs extending further down slope that are easy to trigger.

If triggered the wind slabs may step down to deeper layers resulting in larger avalanches.Minimize overhead exposure during periods of heavy loading from new snow, wind.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

The snow that fell on the Halloween crust became faceted by the early November cold snap. Soft slabs of snow now sit above this weak snow and are becoming increasingly reactive to skier traffic and small triggers such as sluffs out of steep terrain.

Minimize exposure to steep, planar slopes.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 3

Valid until: Nov 20th, 2017 4:00PM