Avalanche Forecast

Issued: Mar 8th, 2012 10:12AM

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

swerner, Avalanche Canada

South Columbia.

Summary

Confidence

Fair - Intensity of incoming weather is uncertain

Weather Forecast

Unstable conditions expected through the weekend. Two cold fronts back to back, will bring light to moderate snow amounts, accompanied by a strong upper SW flow. The Western ranges may see higher snow amounts. The second frontal system looks to be a bit punchier. Friday: Dry in the am. Snow amounts 5-15 cm. Snow continued overnight. Ridgetop winds moderate from the SW. Treeline temperatures near -6. Freezing levels 1200-1400 m. Saturday: Snow amounts 10-20 cm. Ridgetop winds moderate-strong from the SW. Freezing levels 1000-1400 m. Sunday: Light-moderate snow amounts as the front moves through. Freezing levels should drop to 1000 m by Sunday night into Monday.

Avalanche Summary

On Wednesday operators did full explosive testing and reported numerous large avalanches. This may indicate the triggering potential that lies ahead. The snowpack is susceptible to new storm slab, wind slabs, cornice fall, sled and skier triggers. The scary fact is the avalanche size. Even a small avalanche could step down and trigger a persistent weak layer, which in turn will create a large, destructive avalanche. Remote triggered avalanches (from afar) are still being reported up to size 2.5. Many skier triggered size 1-2 avalanches have also been reported. Monday/Tuesday the region saw a widespread natural avalanche cycle in response to snow, wind and warming. With more snow and wind in the forecast the avalanche danger will elevate.

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. A 80-170cm thick slab sits on 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. Easy-Hard test results, with sudden planar shears have been reported on the weak layer. If triggered, the avalanches will be larger than expected. 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

Wind Slabs

Light-mod ridgetop winds from the SW 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

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

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

Expected Size

1 - 5

Valid until: Mar 9th, 2012 8:00AM