Avalanche Forecast

Issued: Feb 19th, 2013 10:04AM

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

jlammers, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Wednesday: Mix of sun and cloud / Light northwest winds / Freezing level at 900mThursday: Very light snowfall intensifying in the evening / Moderate west winds / Freezing level at 800mFriday: Moderate snowfall / Light to moderate southwest winds / Freezing level at 1000m

Avalanche Summary

On Monday a size 2 skier-triggered avalanche occurred near Invermere which resulted in a fatality. The avalanche ran on a south/southeast aspect at 2700m and is thought to have failed at the February 11/12 interface.

Snowpack Summary

Very light amounts of low density snow add to the recently developed storm slab that is between 15-60 cms across the region. The recent storm slab is expected to remain reactive where it is sitting on the weak surface hoar layer that was buried on February 12th. The recent storm slab has also been reactive on Southerly aspects where a sun crust formed during the period from February 8th-11th. Solar radiation or future loading may cause another cycle of natural activity, or an increased sensitivity to human triggers. There are older weak layers that are now buried down around 70-80 cms, and also at about 110 cms. These layers have been less likely to trigger by skiers, but they may still be sensitive to large loads like avalanches in motion or cornice fall.

Problems

Storm Slabs

The buried February 12th surface hoar layer is expected to continue to be reactive. The amount of snow above the weak layer is variable across the region. Watch for increased reactivity with exposure to direct sunlight.

Dig down to find and test weak layers before committing to a line.>The recent snow will require several days to settle and stabilize.>Avoid sun exposed slopes when the solar radiation is strong.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 4

Persistent Slabs

There are a couple of older layers of buried surface hoar and crust combinations that are buried down about 70 cms and 100 cms, that may be triggered by large additional loads.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Valid until: Feb 20th, 2013 2:00PM