Avalanche Forecast

Issued: Mar 24th, 2013 9:12AM

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

pmarshall, Avalanche Canada

Northwest Coastal.

Summary

Confidence

Fair

Weather Forecast

Monday: Light to moderate snowfall – around 10 cm. The freezing level is around 1000 m and winds are moderate to strong from the south-southeast. Tuesday: Clearing through the day. The freezing level is around 1000-1200 m. Winds ease to light from the southwest. Wednesday: A mix of sun and cloud. Temperatures warm slightly with the daytime freezing level jumping to around 1500 m.

Avalanche Summary

Naturally-triggered wind slabs and loose moist avalanches have been observed over the last couple of days. Ice fall also triggered size 2.5-3 avalanches near Bear Pass and other areas. On Saturday there was a report of a size 2 avalanche triggered from a distance on a snowmobile. This slide likely failed on the March 9 surface hoar. Many skier-triggered and skier-remote avalanches of size 1-2.5 were reported last 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. Click here for a full report.

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) has been found at all elevations, but its reactivity is becoming more variable. Whumfing and remote-triggering of avalanches last week indicated the volatility of the layer. A slow improvement is occurring, but confidence is not soaring amongst professionals. Triggering this layer is becoming a low probability but high consequence problem. Check out the Forecaster's Blog for tips on how to deal with this type of problem. 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 new wind slabs forming behind ridges and ribs and in cross-loaded gullies. Cornices are also large and untrustworthy.

Be cautious as you transition into wind affected terrain.>Use ridges or ribs to avoid pockets of wind loaded snow.>Give cornices a wide berth when travelling on or below ridges.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

A layer of surface hoar buried down 50 cm was especially touchy last week. While the likelihood of triggering is slowly dropping, it 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.>Remote triggering is a concern, watch out for adjacent slopes.>Whumpfing is direct evidence of a buried instability.>Choose conservative lines and watch for clues of instability.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 7

Valid until: Mar 25th, 2013 2:00PM