Avalanche Forecast

Issued: Nov 21st, 2017 4:00PM

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

grant statham, Parks Canada

Banff Yoho Kootenay.

The first major avalanche cycle of the season starts on Wed and peaks on Thurs. Avoid all avalanche terrain. There is a significant weak layer deep in the snowpack that is active and we expect widespread avalanche activity over the next two days.

Summary

Weather Forecast

A strong westerly flow dominates the region with the Pineapple Express bringing a big warm up and rain for Wed and Thurs. Expect 20cm of fresh snow by Wed afternoon and warming through the day - by Wed night freezing levels will reach 2600m and Thurs will be a heavy storm day with rain, snow, warmth and strong winds. Cooling beings late Thurs.

Snowpack Summary

The Little Yoho valley has a 100cm snowpack at 1750m. The top 60cm is dry, settled storm snow overlying facets on the Halloween crust - this is the layer to watch. Snowpack tests indicate sudden collapse failures on this layer and propagation can be expected. Strong winds with this next storm will create windslabs in exposed areas at TL and above.

Avalanche Summary

No new avalanche activity observed or reported Tues in the Little Yoho valley, Lake Louise resort or Sunshine Village area. Mon saw significant avalanche activity with Lake Louise ski resort reporting 32 avalanches releasing from 38 target areas controlled; several large avalanches up to size 2.5 - this shows the potential of the Halloween crust.

Confidence

Problems

Persistent Slabs

This is an active avalanche problem and is the main reason people should avoid all avalanche terrain for Wednesday and Thursday. The problem exists in most terrain and will become overloaded with the incoming storm. Watch overhead hazard.

Avoid all avalanche terrain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Wind Slabs

Winds up to 100 km/hr are forecast for Wed and Thurs which will load the new snow onto leeward aspects. Windslabs should be expected near all ridges and gully areas and can be expected to become large once triggered.

Avoid freshly wind loaded features.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Loose Wet

Warming temperatures and rainfall will create wet avalanches in gully areas below treeline. Ice climbers in particular should avoid gully climbs for the next 48-hours.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Nov 22nd, 2017 4:00PM