Avalanche Forecast

Issued: Mar 22nd, 2013 9:45AM

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

Weather Forecast

Saturday: Sunny with light winds. Alpine temperature near -5, dropping overnight.Sunday: Cloud building during the day. Light snow, starting late in the day. Light winds. Alpine temperature near -4.Monday: Light snow. Moderate S winds. Alpine temperature near -4.

Avalanche Summary

Many skier-triggered and skier-remote avalanches of size 1-2.5 have been reported this week, with the bulk of events failing 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.Naturally-triggered wind slabs and loose moist avalanches have also been observed in response to wind loading/ sunshine.

Snowpack Summary

Recent new snow overlies surface hoar, crusts and old wind slabs. New wind slabs have formed lee to SW to NW winds. The surface hoar (buried March 9th; now down about 40-60 cm) is well-developed and fairly widespread at all elevations. Whumfing and remote-triggering of avalanches indicate that this layer is volatile. Professionals are taking a very cautious approach to terrain selection with this in mind. 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

Wind Slabs

Watch for wind slabs behind ridges and ribs and in cross-loaded gullies.

Travel on ridgetops to avoid wind slabs on slopes below.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 4

Persistent Slabs

A volatile layer of buried surface hoar around 50 cm below the surface can be triggered from a distance, propagate across large distances and create surprisingly large avalanches.

Be wary of slopes that did not previously avalanche - even on low angle terrain.>Choose well supported terrain without convexities.>Remote triggering is a concern, watch out for adjacent slopes.>Choose regroup spots that are out of avalanche terrain.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 7

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 23rd, 2013 2:00PM