Avalanche Forecast

Issued: Mar 9th, 2017 4:00PM

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

grant statham, Parks Canada

Banff Yoho Kootenay.

Heading into the weekend, the unstable snowpack compounds on Friday with more snow, increasing winds and a sharp rise in temperature - all three of the big factors. We expect an avalanche cycle on Friday. Watch your exposure carefully, its tricky.

Summary

Weather Forecast

A westerly flow brings another system across the region starting Thursday evening and running until Saturday morning. Friday will be a stormy day; expect another 10 cm at treeline with temperatures rising 10-15 degrees through the day. Winds will also rise, reaching SW 50-75 km/hr at 3000m throughout Friday morning.

Snowpack Summary

50-60cm of storm snow over the past week has been surprisingly reactive. With the addition of more snow on Friday, increasing winds and rising temperatures, the upper meter of the snowpack will continue to produce avalanches on Friday and Saturday. Warming and additional loading may even re-awaken the weak, facetted base which underlies everything.

Avalanche Summary

Large avalanches continue to occur daily.. On the east side of Hwy93N we triggered a size 3 on Mt Hector and a size 2.5 on Dolomite Peak from avalanche control on Thursday - both released in the deep facets. Also a size 3 on Mt Field. Observed numerous recent (last 48 hr) avalanches including several fresh size 2-2.5's above the Dolomite Peak loop.

Confidence

Forecast snowfall amounts are uncertain on Friday

Problems

Wind Slabs

50cm of dry snow from the past week is being blown into cohesive windslabs at higher elevations. Expect these to react easily to triggers, and keep your distance from avalanche starting zones. We have seen long propagations up to 400m this past week.

Be aware of the potential for wide propagations.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Deep Persistent Slabs

The entire snowpack is built upon a structurally weak base, which produces very large avalanches when triggered. There is tremendous uncertainty with this sort of condition, and the only way to hedge against it is to avoid the big avalanche terrain.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.Be aware of thin areas that may propogate to deeper instabilites.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 3

Valid until: Mar 10th, 2017 4:00PM