Avalanche Forecast

Issued: Dec 13th, 2015 8:59AM

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.

The weekend's storm instabilities are expected to linger for a few days.Use extra caution on steep south-facing slopes during the afternoon if the sun is out in full force.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

A ridge of high pressure will bring dry and mostly sunny conditions on Monday. Freezing levels are expected to be around 1000m in the afternoon and ridgetop winds should be light from the north. A mix of sun and cloud is expected for Tuesday with freezing levels falling to valley bottom and light alpine winds from the NW. Light snowfall is being forecast for Wednesday.

Avalanche Summary

On Friday, ski cutting produced size 1 soft slabs in immediate lee features (generally north through east aspects). On Saturday, explosives and ski cutting produced storm slabs size 1-2 which were typically 20-60cm thick. On Sunday, explosives triggered a few size 2 wind slabs which were typically 30cm 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

Recent wind slabs are expected to remain reactive to human-triggering, especially in the leeward side of ridge crests and in wind-loaded chutes. The sun may increase the likelihood of triggering storm instabilities on steep, south-facing slopes.

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

Aspects: North, North East, East.

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 14th, 2015 2:00PM