Avalanche Forecast

Issued: Mar 21st, 2013 10:47AM

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

pgoddard, Avalanche Canada

Northwest Coastal.

Avalanche danger may spike on slopes receiving direct sun. Avoid travelling on or underneath sun-baked terrain.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain for the entire period

Weather Forecast

Friday: No snow. Light N winds. Alpine temperature near -7.Saturday: No snow. Light winds. Alpine temperature near -6.Sunday: Light snow. Light winds. Alpine temperature near -10.

Avalanche Summary

On Wednesday, a skier-remote cornice failure released a size 2 slab on a NW aspect. A skier-remote size 1.5 slab failed on the March 9th surface hoar layer down around 50 cm. Numerous other skier-remote (from up to 800 m away) avalanches of size 2-2.5 also failed just to the NE of the forecast region, on the same layer. A very large (size 3.5) avalanche was triggered in Cherry Bowl in the Shames backcountry on Sunday. ClickÂ hereÂ for a full report. These slides illustrate the ongoing potential for surprising, deep and destructive releases.

Snowpack Summary

30-60 cm of recent storm snow rests on a variety of old snow surfaces, including crusts, previous wind slabs and surface hoar. Warmer temperatures and recent strong winds have now set this new snow into a reactive slab, with wind slabs building in exposed areas on a variety of aspects. The surface hoar (buried March 9th) is reported to be well-developed and fairly widespread, mainly at treeline and alpine elevations. Recent snowpack tests have produced sudden failures (pops/drops) with moderate loading force at this interface. Whumfing and remote-triggering of avalanches indicate that this layer remains volatile. A second surface hoar layer, buried on March 18, is also problematic in some areas. The mid snowpack is generally well settled and strong. Cornices are large and untrustworthy, especially when the sun is out.

Problems

Persistent Slabs

A volatile layer of buried surface hoar around 60 cm below the surface can be triggered from a distance, propagate across large distances and create surprisingly large avalanches.

Remote triggering is a concern, watch out for adjacent slopes.>Avoid open slopes and convex rolls where buried surface hoar may be preserved.>Be wary of slopes that did not previously avalanche - even on low angle terrain.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 7

Wind Slabs

Watch for wind slabs behind ridges and ribs and in cross-loaded gullies. Oscillating winds have left slabs on a variety of slopes.

Avoid freshly wind loaded features.>Use ridges or ribs to avoid pockets of wind loaded snow.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Cornices

Cornices are large and unstable, especially when temperatures become warm or the sun is out. A cornice fall could trigger a large slab avalanche on the slope below.

Avoid steep slopes below cornices.>Stay well to the windward side of corniced ridges.>

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

2 - 6

Valid until: Mar 22nd, 2013 2:00PM