Avalanche Forecast

Issued: Dec 12th, 2015 7:44AM

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

rbuhler, Avalanche Canada

South Rockies.

Touchy avalanche conditions exist from all the recent snowfall. Use a cautious approach in the mountains this weekend.

Summary

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

The last of the Pacific storm pulses is expected to hit the region Saturday overnight. Around 10cm of snowfall is expected with freezing levels around 1200m. Light scattered snowfall may continue through the day on Sunday. Alpine winds are expected be strong from the SW in the morning but will ease in the afternoon. Monday is expected to be dry with a mix of sun and cloud. Freezing levels are forecast to drop to near valley bottom and alpine winds should be light from the NW. Tuesday looks to be similar with mainly dry condition and a mix of sun and cloud.

Avalanche Summary

Reports from Thursday include a remotely triggered Size 1.5 slab avalanche from a snowmobiler on a sheltered north facing slope below treeline that ran on surface hoar buried early-December. On Friday, ski cutting produced size 1 soft slabs in immediate lee features (generally north through east aspects).

Snowpack Summary

Continued snowfall brings total treeline snowpack depths to over 1m, with even more in the alpine, but it diminishes quickly below around 1700m. Recent rain created a near surface crust as high as 1800m (or higher in the southern part of the region). Above that elevation, storm and wind slabs are bonding poorly to the old snow surface buried early December, which is probably a crust and/or a combination of facets and buried surface hoar now down around 40-60cm in sheltered treeline areas. The buried surface hoar may be well preserved in sheltered areas, creating particularly touchy slabs with the potential for remote triggering, extensive releases and prolonged sensitivity to triggering. Below that a thick weak layer of facets may be lurking around the thick mid-November crust.

Problems

Wind Slabs

New snow will likely be sensitive to human triggers, and particularly deep and weak on the leeward side of ridge crests and in wind-loaded chutes.

Avoid freshly wind loaded features.>Be cautious as you transition into wind affected terrain.>

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

The weakness buried early-December is becoming more stubborn to trigger, but lingering pockets of buried surface hoar and facets may maintain touchy conditions on sheltered slopes, especially in the 1700-2100m elevation range.

Avoid open slopes and convex rolls at and below treeline where persistent weaknesses may be preserved.>Make observations and assess conditions continually as you travel.>Dig down to find and test weak layers before committing to a line.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Valid until: Dec 13th, 2015 2:00PM