Avalanche Forecast

Issued: Dec 11th, 2018 4:00PM

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

lisa paulson, Parks Canada

Banff Yoho Kootenay.

Building hazard with flurries & wind tonight and Thursday. The new snow will be great for ski conditions, but will make for touchy avalanche conditions as it lands on a weak base.

Summary

Weather Forecast

Flurries will continue tonight, expect up to 10-15 cm. After a break on Wednesday, flurries return for Thursday where another 10-30 cm may fall by Friday evening. The greatest amounts will be west of the divide. Temperatures should remain cold throughout, winds will be moderate to strong W/SW during each snow event.

Snowpack Summary

Up to to 10 cm of new snow has fallen so far. Its buried a widespread weak layer of surface hoar/facets and is building new wind slabs with moderate SW winds in the immediate lees. The new snow will sit on a generally weak snowpack, with the October 26th crust/facet layer being up to ~30 cm above ground. Snow depths range from 50-85 cm at 2000 m.

Avalanche Summary

No new avalanches reported or observed today, but as recently as Saturday someone triggered a nasty looking size 2 on the SE slopes of Cirque Fore-Peak at 2700m above Helen Lake. Two skiers were caught on the flanks of a slab 20-40cm deep, 80m wide, running up to 250m with no burial but they some lost equipment.

Confidence

Intensity of incoming weather systems is uncertain

Problems

Wind Slabs

Newly formed wind slabs will likely not bond well to underlying surfaces. They rest on old slabs, up to 40 cm deep. These slabs can provide the push to get the deep persistent slab problem initiated or entrain the weak faceted snowpack.

If triggered the wind slabs may step down to deeper layers resulting in larger avalanches.Use caution in lee areas. Recent wind loading have created wind slabs.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Deep Persistent Slabs

As load increases through the week, it may become more reactive in isolated, steep spots & adjacent to thin rocky areas. Be cautious in steep terrain where a stiffer, more cohesive slab exists over the weak faceted snow at the base of the snowpack.

Be aware of thin areas that may propogate to deeper instabilites.Whumpfing is direct evidence of a buried instability.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1.5 - 2

Valid until: Dec 12th, 2018 4:00PM