Avalanche Forecast

Issued: Dec 21st, 2018 4:00PM

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

stephen holeczi, Parks Canada

Banff Yoho Kootenay.

Nice weather Saturday but there are two significant weak layers in the snowpack and some fresh wind slabs. Natural activity will likely taper, but the snowpack is primed for human triggering. SH

Summary

Weather Forecast

Mainly sunny skies and cold (-15Â°c to -20Â°c) for Saturday. Winds will diminish and be light to moderate from the NW. Some light snow Sunday but overall no major systems in the forecast for the next week.

Snowpack Summary

An average 40-80 of recent storm snow with variable wind effect now sits over the Dec 10th facet/surface hoar interface. In many areas the lower snowpack is weak with the October 26 depth hoar, facets and crust near the base. Snow pack depths range from 90-160 cm at ~2000 m.

Avalanche Summary

Numerous natural avalanches up to size 2.5, as well as several skier remote and skier triggered avalanches up to size 2 have been observed in the last several days. One explosive controlled avalanche today at Sunshine Village went close to 2m deep on the basal weakness. This pattern is likely to continue for the next while.

Confidence

Problems

Deep Persistent Slabs

Recent snow has now overloaded the Oct. 26 deep persistent layer of facets and depth hoar, and there is enough mass now to cause large avalanches.

Good day to make conservative terrain choices.Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1.5 - 3

Persistent Slabs

The Dec. 10 persistent layer of facets and surface hoar is now buried 40 - 80cm. Avalanches have either been independently running on this layer, or stepping down to the basal weakness.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2.5

Wind Slabs

Fresh wind slabs from strong winds over the last 2 days have formed within the new storm snow. These will be most prevalent in the lee of features and may stay reactive over the next couple of days.

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

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

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