Avalanche Forecast

Issued: Dec 22nd, 2012 9:25AM

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

ghelgeson, Avalanche Canada

Purcells.

Summary

Confidence

Good

Weather Forecast

Saturday night: 4 - 10 cm Sunday: Moderate SW ridge top winds easing throughout the day. Isolated flurries. 1500m temp: -5 Freezing level: SurfaceMonday: Light S ridge top winds. 1500m temp -9. No snow.Â Freezing Level: SurfaceTuesday:Â Light S ridge top winds. Treeline temp -12. No snow.Â Freezing Level: Surface

Avalanche Summary

We're starting to see the effect of the big winds midweek. We're getting observations from across the region of a recent natural avalanche cycle to size 2. These avalanches are coming from Alpine terrain facing NW, N & NE.Â

Snowpack Summary

In the last 72 hours storm snow totals in the north are between 30 - 50 cm while the south of the region has seen closer to 80 cm near the Purcell Wilderness Conservancy. This adds to the abundance of storm snow that's fallen in the last 10 days. Strong winds on Wednesday/Thursday wreaked havoc in the alpine creating wind slabs capable of failing as large avalanches.Â Cornices are also a problem at the highest elevations.Â The mid-pack is reported to be settling well.Â I haven't heard of any test results on the late November surface hoar in the last few days.Â The early November crust, near the base of the snowpack has also been inactive as of late. It's important to note that professionals are still cautious about these lingering persistent slab problems, but the likelihood of triggering is low. Be wary of steep complex terrain with a shallow snowpack, where triggering a persistent weakness is more likely.

Problems

Wind Slabs

Wind slabs in the Alpine are a serious concern. I suspect they're susceptible to human triggering and when they fail, they will go big. Watch for wind slabs immediately below ridge crest and in the lee of mid slope terrain features like ribs

Slopes above treeline still need a few days to stabilize. Those without significant experience and expert terrain management should avoid alpine terrain.>If you see signs of wind loading, or you feel the snow stiffen under your skis or machine, back off and head to wind sheltered terrain.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 6

Cornices

New snow and wind has fueled significant cornice growth. The right chunk of falling cornice has the potential to kick off a wind slab avalanche.

Give cornices a wide berth when traveling on ridges.>

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Likely

Expected Size

1 - 3

Valid until: Dec 23rd, 2012 2:00PM