Avalanche Forecast

Issued: Dec 10th, 2018 4:00PM

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

ian jackson, Parks Canada

Banff Yoho Kootenay.

A storm is coming, but most of the precip is coming later in the day Tuesday, so not much change until Wednesday. This 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

Finally, snow is in the forecast! We should see light snow starting on Tuesday with only small accumulations ~ 5cms. An additional 10-15 cms by Wednesday PM and up to 40 cms by Thursday. The greatest amounts will be west of the divide. Temperatures should remain cold throughout, but winds will be strong W/SW with the highest on Tuesday and Thurs

Snowpack Summary

A cm or two of new snow is covering up widespread surface hoar and facets in most places. In exposed alpine areas, old wind slabs 10-40 cm deep linger in immediate lees. 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

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

Timing, track, or intensity of incoming weather system is uncertain

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 11th, 2018 4:00PM