Avalanche Forecast

Issued: Dec 15th, 2015 7:23AM

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

triley, Avalanche Canada

South Rockies.

Wind slabs may exist on several aspects in the alpine and at treeline. Light additional loads like a single skier may be enough to trigger these weak pockets.

Summary

Confidence

Moderate - Track of incoming weather systems is uncertain on Friday

Weather Forecast

Light to moderate winds overnight combine with 5-10 cm of new snow and alpine temperatures around -18. Clearing trend on Wednesday should provide broken skies at least by the afternoon. Clear and cold overnight with cloud and strong southwest winds developing on Thursday. The next Pacific moisture should move into the region by Friday.

Avalanche Summary

On Monday, a couple of size 2 avalanches were reportedly triggered by skiers in steep north and northeast facing slopes. Over the weekend, explosives and ski cutting produced storm slabs size 1-2 which were typically 20-60cm thick.

Snowpack Summary

The series of storms last week produced 70-90cm of new snow in the region. A rain crust which formed during the middle of the storm is now down 40-60cm and has become the primary layer of concern during the weekend storm. The early December interface consists of crust, surface hoar, and/or facets and is typically down 70-90cm. Around 20-30cm below this interface is a rain crust from mid-Nov with a thick layer of facets below it. Both the early-Dec and mid-Nov layers have become dormant and are likely being capped at treeline and below by the more recent rain crust layer. However, these layers may still be reactive to heavy triggers such as cornices, explosives, or smaller avalanches stepping down.

Problems

Wind Slabs

Pockets of wind slab may be found on several aspects in the alpine and at treeline due to changing wind directions and loose snow available for transport.

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

A weakness buried early-Dec and a rain crust from mid-Nov in the mid-pack are becoming difficult to trigger but are still a concern in isolated areas. Heavy triggers like cornices or avalanches stepping down could result in very large avalanches.

Dig down to find and test weak layers before committing to a line.>Avoid open slopes and convex rolls at and below treeline where persistent weaknesses may be preserved.>Caution around convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Valid until: Dec 16th, 2015 2:00PM