Avalanche Forecast

Issued: Dec 1st, 2011 8:44AM

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

ghelgeson, Avalanche Canada

Purcells.

Tricky avalanche conditions require extensive experience to travel safely at and above treeline this weekend.

Summary

Confidence

Fair - Due to limited field observations

Weather Forecast

Friday: A cold front sweeps across the region Thursday night lingering into the first half of Friday bringing light precipitation & big winds out of the NW clocking in at 60 - 90 km/h. No significant precipitation is expected out of the system. Temps are forecasted to stay steady around -6 @ 1500m on Friday.Saturday: High pressure builds back into the region Saturday keeping the region dry through the weekend under scattered clouds. Freezing levels will stay near valley bottom but an inversion is forecasted for the area bringing above freezing temperatures between 1800m & 2300m Sunday & Monday.

Avalanche Summary

Numerous size 2 -2.5 avalanches have been reported failing both naturally & with the aid of explosives on high elevation north through east facing slopes.

Snowpack Summary

Snow depths are variable throughout the region. In the alpine there is 170- 250cm. At treeline depths vary from 130-150cm. Sunday's warm, moist storm combined with strong southwesterly winds created stiff wind slabs on north through east facing slopes. Winds shifted to the North Wednesday creating a reverse load. Now there are a wide variety of windslabs at and above treeline on all aspects.Conditions are primed for human triggered avalanches at and above treeline due to weak sugary snow at the ground combined with tricky wind slabs. The upper snowpack is tightening up forming a stronger mid-pack, but if an avalanche is triggered in the upper layers or initiated from a shallower spot in the snowpack it could step down to weak basal facets at the ground creating large and unmanageable avalanches with very high consequences.

Problems

Wind Slabs

Winds blowing from around the compass have created a windslab problem that exists on all aspects at and above treeline. Assessing the variability in this problem is proving tricky, even for very experienced folks in the region.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

While patchy in distribution, weak basal layers in the snowpack could fail under the stress of the strong slab above producing large full depth avalanches. Riders should continue to be concerned about the potential for high consequence avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 6

Valid until: Dec 2nd, 2011 8:00AM