Avalanche Forecast

Issued: Nov 20th, 2017 4:00PM

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

ian jackson, Parks Canada

Banff Yoho Kootenay.

A brief reprieve from storm systems, but the next one on Wednesday looks warm. Enjoy the good snow for one more day, but be careful as the Halloween crust/ facet layer is spooky!

Summary

Weather Forecast

Tuesday is a rest between storms with light winds, cool temps and precip starting in the afternoon (10 cm overnight). Wednesday is looking to be quite warm with freezing levels rising to ~ 2500m and rain at lower elevations.Â Temps will cool on Thursday with freezing levels dropping to ~ 2000m and 20- 30 cm of snow.

Snowpack Summary

30 - 70 cms of new snow over the last 5 days has been blown into windslabs up to 1 meter deep in the alpine. Where windslabs don't exist, this snow has formed a 30-60 cm slab that sits on the Halloween crust/facet interface. This interface is a crust below ~ 2400m on polar aspects and higher on solar aspects. Total snowpack at treeline is 80-100 cm

Avalanche Summary

Lots of avalanche activity on Monday. Some examples: -Widespread natural activity up to size 2.5 on the National Geographics and Whitehorn gullies in the Lake Louise ski hill and backcountry-A size 3 on a NE aspect of Pilot mountain with a ~ 500m fracture line. Many of the avalanches initiated in the low alpine where the halloween crust exists

Confidence

Due to the number of field observations on Monday

Problems

Persistent Slabs

30 - 60 cms of snow from the last storm has settled into a slab that overlies the Halloween crust/ facet interface. A natural avalanche cycle occurred on this layer on Sunday and Monday with avalanches to size 3, mostly starting in the low alpine.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.Avoid areas with overhead hazard.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 3

Wind Slabs

Strong SW winds on Sunday created windslabs up to 1 meter thick in exposed alpine areas. If triggered, these will likely step down to the Halloween crust/ facet layer, creating a much larger avalanche.

Avoid freshly wind loaded features.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Nov 21st, 2017 4:00PM