Avalanche Forecast

Issued: Dec 8th, 2018 4:00PM

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

tim haggarty, Parks Canada

Banff Yoho Kootenay.

Flights today along the 93N found several instances of small windslabs triggered by skiers that appeared to have stepped down to the deep persistent layer.

Summary

Weather Forecast

One more night of cold temperatures reaching -20C in valley bottoms with an inversion allowing temps near -10C at 2000m. A Pacific trough will push the current ridge out of the way Sunday bringing cloud and a warming trend that will break down the inversion. Up to 5cm of snow is possible on Monday and another 10cm is possible overnight Tuesday.

Snowpack Summary

No new snow in several days. Old wind slabs 10-40cm deep linger in immediate lee areas of the alpine. The October 26th crust/facet layer is ~30 cm above ground. In many areas the entire snowpack is faceting and becoming quite weak. Snow depths range from 50-85 cm at 2000 m.

Avalanche Summary

Another skier accidental today 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 some lost equipment. This slab was certainly originated as a windslab in the immediate lee of the ridge but definitely scrubbed down to facets

Confidence

Intensity of incoming weather systems is uncertain on Tuesday

Problems

Wind Slabs

These are getting quite old but are up to 40 cm deep in the immediate lees of alpine features. Although small in size, these slabs can provide the push to get the deep persistent slab problem initiated.

If triggered the wind slabs may step down to deeper layers resulting in larger avalanches.

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

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 1.5

Deep Persistent Slabs

It is still possible to trigger this layer but it will be in isolated, steep spots and often 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.

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

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1.5 - 2

Valid until: Dec 9th, 2018 4:00PM