Avalanche Forecast

Issued: Feb 20th, 2013 9:00AM

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

jlammers, Avalanche Canada

South Columbia.

Summary

Confidence

Fair - Intensity of incoming weather is uncertain on Friday

Weather Forecast

Thursday: Light snowfall intensifying in the evening / Moderate southwest winds / Freezing level at 900mFriday: Heavy snowfall / Strong southwest winds / Freezing level at 1000mSaturday: Light snowfall / Moderate northwest winds / Freezing level at 700m

Avalanche Summary

Recent explosives control produced slab avalanches to size 2.5. The avalanches occurred on a variety of aspects at treeline and in the alpine and are suspected to have ruin on the February 12th interface. A recent natural cornice fall also pulled out a size 2 slab on the slope below.

Snowpack Summary

Variable amounts of low density snow add to the recent storm slab that is between 20-50 cms across the region. These light accumulations may overlie wind slabs which formed a few days ago in the alpine and at treeline. 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. Future loading on the recent storm 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 60-80 cms and also at about 110 cms. These layers have been unlikely to trigger by skiers, but they may still be sensitive to large loads like avalanches in motion or cornice fall.

Problems

Storm Slabs

This storm slab is expected to continue to be reactive to the weight of a skier/rider where it overlies a weak layer of surface hoar and sun crusts that was buried on February 12th.

Dig down to find and test weak layers before committing to a line.>Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 5

Wind Slabs

New wind slabs are expected to develop on Thursday with light snowfall and moderate winds. These new wind slabs may hide older wind slabs that formed a few days ago.

Stay off recent wind loaded areas until the slope has had a chance to stabilize.>Be cautious as you transition into wind affected terrain.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

There are older layers of buried surface hoar and crusts that are unlikely to be triggered by the weight of a skier or sledder, but may be triggered by large additional loads like cornice fall or a slab avalanche in motion.

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

Expected Size

3 - 6

Valid until: Feb 21st, 2013 2:00PM