Avalanche Forecast

Issued: Nov 21st, 2018 4:00PM

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

ian jackson, Parks Canada

Banff Yoho Kootenay.

If we get more snow than forecasted, watch for touchy storm slabs as it is falling on a widespread surface hoar layer. This may become a layer to watch if it's not all blown away before it is buried.

Summary

Weather Forecast

A SW flow is bringing some precipitation our way. Models are showing 2-10 cm on Thursday and an additional 5 cm on Friday. Northern areas should see the highest snow amounts. Winds should ease to moderate from the SW with the incoming storm and then switch to NW with colder temps on Friday midday. Saturday looks colder and drier.

Snowpack Summary

15-30 cm of facetted surface snow with surface hoar forming at all elevations. Wind effect at treeline and above has scoured ridge crests and created wind slabs in the alpine. The Oct 26 crust is roughly 30 cm above the ground with facets above and below it. It is present up to 2800m on shady aspects, and at higher elevations on solar aspects

Avalanche Summary

A large avalanche was observed on the N face of Mt. Stanley. Forecasters on a trip into the lake louise backcountry on Tuesday had several whumphs in alpine and treeline areas that had been wind affected and remote triggered a size 2 on a NE aspect at 2300m that failed on facets near the ground

Confidence

Intensity of incoming weather systems is uncertain on Thursday

Problems

Deep Persistent Slabs

We are seeing occasional skiier triggered , and explosive controlled avalanches on the Oct 26 crust at local ski areas. This problem seems to be most reactive in areas where the wind has created more of a slab on top of it.

Whumpfing is direct evidence of a buried instability.If you are increasing your exposure to avalanche terrain, do it gradually as you gather information.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1.5 - 2.5

Wind Slabs

The wind slab problem seems to be most active in Eastern areas where there was more wind effect during the Nov. 18th. wind event.

If triggered the wind slabs may step down to deeper facet layers resulting in larger avalanches.Be careful with wind loaded pockets, especially near ridge crests and roll-overs.

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

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

Valid until: Nov 22nd, 2018 4:00PM