Avalanche Forecast

Issued: Apr 15th, 2013 11:10AM

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

pgoddard, Avalanche Canada

Purcells.

This bulletin was produced using limited data streams, and significant variations in snowpack structure are likely to exist. If you've been traveling in the backcountry, we'd love to hear from you. Observations can be sent to forecaster@avalanche.ca.

Summary

Confidence

Poor - Due to variable snowpack conditions

Weather Forecast

Tuesday: No snow. Moderate E winds. Freezing level near 1200 m, dropping to 200 m overnight.Wednesday: Light snow. Light W winds. Freezing level near 1500 m, dropping to 1100 m overnight.Thursday: Light snow. Light W winds. Freezing level near 1700 m, dropping to 1100 m overnight.

Avalanche Summary

On Sunday, a naturally triggered size 2.5 slab failed on a buried crust. Numerous small loose dry avalanches were also observed. In neighbouring Glacier National Park, skiers triggered a size 3 slab on a buried crust on an east aspect in the alpine on Monday. The slab above this interface may be reaching tipping point with incremental loading from snow and wind.

Snowpack Summary

Around 40 cm recent storm snow has been shifted by variable winds into wind slabs at treeline and above. In some areas, a trace of new snow overlies a refrozen surface on southerly aspects and below 2000 m on northerly aspects. A weak interface in the upper metre of the snowpack consists of a crust on solar aspects, and surface hoar on high-elevation northerly aspects. Recent activity in Glacier National Park and the North Columbia regions demonstrates that this interface has the potential for surprisingly large avalanches. Cornices in the region are 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

Likely - Very Likely

Expected Size

1 - 4

Persistent Slabs

A weak interface buried in the upper metre of the snowpack can create surprisingly large avalanches. It`s been reactive in nearby regions, but there`s limited information about its reactivity in the Purcells. Be cautious in alpine terrain.

Choose well supported terrain without convexities.>Be aware of the potential for large, deep avalanches due to the presence of buried weak layers.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 6

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