Avalanche Forecast

Issued: Mar 7th, 2012 10:26AM

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

Avalanche Canada swerner, Avalanche Canada

If sunny skies, and solar radiation occur. Southerly slopes may deteriorate, and natural avalanche activity could spike.

Summary

Confidence

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

Weather Forecast

A ridge of high pressure moves inland bringing dry, warming conditions until Friday. A frontal system tracks inland from the coast, allowing a southwesterly flow and unsettled conditions. Thursday: Dry, mix of sun and cloud. Ridgetop winds moderate from the West. Treeline temperatures near -3. Freezing levels 12-1500 m. Friday: Snow amounts near 10 cm. Ridgetop winds moderate SW. Treeline temperatures near -5. Freezing levels 1100-1300 m. Saturday: Light snow in the am, moderate amounts in the evening. Freezing levels 1300 m.

Avalanche Summary

On Monday/Tuesday the region saw a widespread natural avalanche cycle in response to snow, wind and warming. Operators are reporting numerous size 1-3.5 natural avalanches, starting in the alpine on all aspects, and running full path. Rider triggered slabs were also reported in the size 1-2 range, failing on storm snow weaknesses. There are still reports of remotely triggered avalanches up to size 2.5 on suspected mid-February SH interface. The region has seen a widespread cycle since last Saturday. With more snow and wind in the forecast the avalanche danger will elevate. This could be the story for all elevations.

Snowpack Summary

The weekend past, up to 80 cm of storm snow fell. Strong winds from the SW and fluctuating temperatures were the perfect recipe for storm slab, and wind slab instabilities. This new snow has buried variable old surfaces (surface hoar, facets, and crusts) that formed mid-February. These persistent weak layers have remained touchy all week and are a key concern at all elevations. If triggered, the avalanches will be larger than expected. Sunny, clear skies are likely to exist through Thursday. Moist-wet snow surfaces, snowballing, and point release (loose wet slides started from a point, gathering mass in a fan-like shape) are indicators of a deteriorating upper snowpack. I'd be weary of south facing slopes, affected by solar radiation. There may even be step-down potential on deeply buried weak layers. Large cornices have formed and loom as potential triggers on the slopes below.

Problems

Storm Slabs

An icon showing Storm Slabs
Storm snow with fluctuating temperatures are the perfect recipe for storm slab development. Storm slabs could step down to a persistent weak layer, creating surprisingly large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 5

Wind Slabs

An icon showing Wind Slabs
Light-moderate W-N ridgetop winds have created new wind slabs on lee slopes. Wind slabs are touchy, and exist on most aspects, hiding behind terrain features, even at treeline. Cornices have formed, they may act as a large trigger on slopes below.

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 5

Persistent Slabs

An icon showing Persistent Slabs
Persistent weak layers, found at all elevations, are tricky to manage. 80-170 cm of snow now sit on this interface, the additional stress of a storm or wind slab release, sled or skier may be the tipping point, creating surprisingly large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 7

Valid until: Mar 8th, 2012 8:00AM

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