Avalanche Forecast

Issued: Apr 15th, 2013 11:13AM

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.

pgoddard, Avalanche Canada

South Columbia.

Summary

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Tuesday: No snow. Moderate E winds. Freezing level near 1300 m. Wednesday: Light snow. Light SW winds. Freezing level near 1500 m. Thursday: Light snow. Light SW winds. Freezing level near 1600 m.

Avalanche Summary

Several size 1 wind slabs were triggered naturally by wind-loading on Monday. Explosives testing in the south of the region produced slabs up to size 2.5 failing on a crust in cliff terrain. A skier triggered a size 2 cornice and loose snow avalanche on a NE aspect at 2400 m on Sunday.Neighbouring regions: In Glacier National Park, skiers triggered a size 3 slab on a buried crust on an east aspect in the alpine on Monday. On Sunday in the North Columbia region, a helicopter remotely triggered a size 3 slab from 50 m away. It failed on a west aspect at 2450 m, on a crust buried down 60 cm. I suspect these were the same interface. This interface also exists in the South Columbia region.

Snowpack Summary

Up to 40 cm recent storm snow has been shifted by variable winds into reactive wind slabs at treeline and above. A weak interface down about 60-120 cm consists of a crust on solar aspects, and surface hoar on high-elevation northerly aspects. Cornices in the region are very large and potentially destructive. Periods of warming or solar radiation may increase the reactivity of cornices and storm slabs.

Problems

Wind Slabs

Recent snowfall has been redistributed by changing winds. Wind slabs exist on a variety of aspects at treeline and above. Wind has also formed very large and potentially unstable cornices.

Stay off recent wind loaded areas until the slope has had a chance to stabilize.>Use ridges or ribs to avoid pockets of wind loaded snow.>Give cornices a wide berth when travelling on or below ridges.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Persistent Slabs

A weak interface buried down about 60-120 cm has been creating surprisingly large avalanches in neighbouring regions. Incremental loading by snow and wind may have brought the slab above this layer closer to its tipping point.

Choose well supported terrain without convexities.>Be aware of the potential for large, deep avalanches due to the presence of buried weak layers.>Click the Details Tab (above) for more information.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 6

Valid until: Apr 16th, 2013 2:00PM