Avalanche Forecast

Issued: Dec 11th, 2015 7:55AM

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

ccampbell, Avalanche Canada

South Rockies.

Touchy avalanche conditions with all the recent snow. Use a cautious approach in the mountains this weekend.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Saturday: Increasing cloud and wind with flurries in the afternoon and freezing level remaining in valley bottoms. Sunday: 5-10cm of fresh snow possible by Sunday morning, with another 5-10cm throughout the day. Freezing level near valley bottom with moderate to strong southwesterly ridgetop winds. Monday: Another 2-5cm of snow with cooler temperatures and light westerly winds.

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. Other reports included more evidence of a large natural avalanche cycle at alpine and treeline elevations on Tuesday and Wednesday.

Snowpack Summary

Continued snowfall brings total treeline snowpack depths to over a metre, 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

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.

Make observations and assess conditions continually as you travel.>Avoid open slopes and convex rolls at and below treeline where persistent weaknesses may be preserved.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 5

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.

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

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Dec 12th, 2015 2:00PM