Avalanche Forecast

Issued: Dec 19th, 2015 8:47AM

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

jlammers, Avalanche Canada

South Columbia.

New snow and extreme ridgetop winds will keep the Avalanche Danger elevated on Sunday. Watch for continued wind slab development throughout the day.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Sunday

Weather Forecast

Between 5 and 15cm of new snow and strong to extreme southwest ridgetop winds are expected on Sunday. Continued light flurries and moderate southwest winds will persist for Monday and Tuesday. Freezing levels should sit at valley bottom for all 3 days. For a more detailed weather overview, check out our Mountain Weather Forecast at avalanche.ca/weather.

Avalanche Summary

Recently, natural and human-triggered wind slab avalanches in the size 1-1.5 range were observed in the alpine and at treeline. Continued strong winds and new snow will likely be the driver for continued wind slab avalanche activity over the next few days.

Snowpack Summary

Steady flurries over the past few days and moderate southwest winds have formed fresh wind slabs in exposed lee features in the alpine and at treeline. Between 80 and 120cm below the surface you'll likely find a weak layer of well-developed surface hoar. This layer is most widespread and reactive at lower elevations (between 1400m and 1800m.) Snow pit tests suggest that human triggering of this interface is becoming unlikely. That said, if it does fail the overlying slab is stiff enough to propagate over a wide distance. Below this layer, the snowpack is thought to be generally strong and well-settled.

Problems

Wind Slabs

Even if new snow amounts are modest in your riding area, there's plenty of loose snow on the ground for redistribution by forecast strong winds on Sunday. Watch for new wind slab development at treeline and in the alpine.

Be cautious as you transition into wind affected terrain.>Stay off recent wind loaded areas until the slope has had a chance to stabilize.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

A layer of buried surface hoar can be found between 1400m and 1800m. Although this layer has become less likely to trigger, I'd remain cautious on steep roles in cut-blocks and open glades below treeline.

Conditions are greatly improved, but be mindful that deep instabilities are still present below treeline.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Valid until: Dec 20th, 2015 2:00PM