Avalanche Forecast

Issued: Mar 21st, 2012 10:43AM

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

Avalanche Canada pgoddard, Avalanche Canada

Be wary of any slopes receiving direct sun. Solar warming could trigger avalanches or weaken existing slabs.

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain

Weather Forecast

Thursday: Light snow. 5-10cm. Light to moderate south-west winds. Freezing level valley floor.Friday/Saturday: Clear and sunny. Light winds. Afternoon temperatures rising on sunny slopes, with the freezing level falling to valley floor at night.

Avalanche Summary

On Tuesday, a number of size 1-1.5 avalanches were triggered in the storm snow naturally and by people. The frequency of deep releases on the February persistent weakness has gone down, with the most recent reports occurring at the weekend (size 3-3.5 slabs, 100-180 cm deep). There were also two size 3 avalanches that were triggered accidentally by snowmobilers just south of the region near Kimberley on Sunday. I'm concerned about strong solar warming on Friday and Saturday potentially triggering cornice fall or surface avalanches, which could step down to the Feb weakness, leading to very large releases.

Snowpack Summary

South to south-westerly winds combined with new snow have created wind slabs in the alpine and at treeline. Sunny periods on Sunday developed a sun-crust on southerly aspects up well into the alpine. Older storm snow is reported to be bonding well to underlying surfaces. A key concern is a persistent weak layer of buried surface hoar from mid-February that is buried 1-2 m deep. Snowpack tests give sudden "pops" results on this layer, indicating the ongoing potential for very large avalanches. Because the layer is so deeply buried, it's unlikely to fail without a large trigger (e.g. cornice fall or explosive). However, there's always the chance of someone stumbling across a sweet spot, particularly in shallow snowpack areas.

Problems

Wind Slabs

An icon showing Wind Slabs
Wind slabs can be found in the alpine and at treeline, behind ridges and terrain breaks. Very large cornices also threaten slopes below.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Storm Slabs

An icon showing Storm Slabs
Storm snow may sluff easily or fail as a slab, especially in steep or convex terrain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Deep Persistent Slabs

An icon showing Deep Persistent Slabs
Reports of avalanches releasing on the mid-February weak layer are becoming less frequent. Large triggers like cornice falls may release the slope below, resulting in very large destructive avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

3 - 9

Valid until: Mar 22nd, 2012 9:00AM

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