Avalanche Forecast

Issued: Nov 23rd, 2018 4:00PM

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

tim haggarty, Parks Canada

Banff Yoho Kootenay.

While the windslabs are getting older, they form a reactive slab over the deep persistent layer.

Summary

Weather Forecast

Expect the light winds to shift to the North tonight as arctic air pushes south into the region Friday evening. This will squeeze a few more flakes of snow out of the clouds and drop temperatures a few 4 or 5 degrees for a high of around -8C at 2000m Saturday.

Snowpack Summary

5cm of new snow now buries surface hoar, thin suncrusts, and previous wind effect. Aging windslabs sit over a faceted midpack above the october 26 facet and crust interface generally found 10 to 30 cm above the ground.

Avalanche Summary

Lake Louise reported a sz 2 slab failing on the October 26 layer on the N aspect of Whitehorn. While efforts yesterday had failed to initiate an avalanche higher in the start zone, a 1 kg charge placed lower did the trick today with the thought that winds strong winds had created the slab lower in the start zone instead of the immediate lee.

Confidence

Due to the number of field observations

Problems

Deep Persistent Slabs

We were 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

While these slabs are getting fairly old, they remain significant as they have contributed to a reactive slab above the October 26 crust. A few cm of snow will now hide these slabs making them a bit harder to detect and avoid.

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 24th, 2018 4:00PM