Avalanche Forecast

Issued: Dec 23rd, 2012 8:49AM

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

ghelgeson, Avalanche Canada

Purcells.

Lower danger ratings in the alpine should not be seen as carte blanche for bigger terrain. See the forecaster's blog for some ideas about approaching the mountains this week.

Summary

Confidence

Good

Weather Forecast

Monday: Light ridgetop winds out of the E. No Snow. 1500m temp: -15 Freezing level: SurfaceTuesday: Light SE ridge top winds. 1500m temp -13 No snow.Â Freezing Level: SurfaceWednesday:Â Light SW ridge top winds. Treeline temp -13. No snow.Â Freezing Level: Surface

Avalanche Summary

No large avalanches were reported yesterday.Â There were however a few reports of both natural and skier triggered avalanches to size 1.5 in wind loaded features.Â Cornices were also reported to be touchy in the north of the region.

Snowpack Summary

In the last four days the north of the region received 30 - 50 cm while the zone closer to the Purcell Wilderness Conservancy received closer to 80 cm. Winds picked up Wednesday/Thursday of last week forming large wind slabs in the Alpine that produced a limited avalanche cycle to size 2 that persisted through Friday.Â It sounds like these slabs are settling out but I'm still suspect of them, especially on steep unsupported features. New (relatively) thin wind slabs involving Saturday nights snow may still be an issue Monday. Cornices are also a problem at the highest elevations. The mid-pack is reported to be settling well. I haven't heard of any test results involving the late November surface hoar in the last five days. 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

In the alpine wind slabs up to 70 cm in depth are still a concern, especially in steep unsupported terrain. Pay attention to what the winds are doing. Even a short burst of wind has the potential to create touchy shallow wind slabs.

Be cautious as you transition into wind affected terrain.>If you venture into the open, start with small, low consequence terrain. You need to carefully evaluate how the upper 75 cm of the snowpack is behaving before committing to more serious lines.>

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 6

Cornices

New snow and wind has fueled significant cornice growth. Although unlikely, the right chunk of falling cornice has the potential to kick off a wind slab avalanche in steep terrain.

Extra caution needed around cornices with current conditions.>

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 3

Valid until: Dec 24th, 2012 2:00PM