Avalanche Forecast

Issued: Mar 8th, 2012 8:53AM

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

Avalanche Canada ccampbell, Avalanche Canada

Summary

Confidence

Fair - Intensity of incoming weather is uncertain for the entire period

Weather Forecast

Friday: Heavy snow and strong southwesterly winds. 30-40cm possible by the end of the day for immediate coastal areas, but expected to be dryer inland. Freezing levels are expected to drop to 1000m. Saturday and Sunday: Continued moderate snowfall and strong south to southwest winds with freezing levels remaining in the 500-1000m range.

Avalanche Summary

We received an initial report of an avalanche fatality in the Brandywine area on Tuesday. So far we know that a single snowmobiler was buried and perished in a Size 3 avalanche. The avalanche occurred on an east aspect at approximately 1700m, the slab was estimated to be 1.5-2.0m thick and 400m wide and suspected to have stepped-down to the mid-February persistent weakness. We will provide more details as they come available. More reports of last weekend's widespread large natural avalanche cycle are coming in with observations of Size 4.5 avalanches. Some of the larger slabs propagated 2-3Km along ridgelines and stepped down to the mid-February persistent weakness, and there's no reason why similar avalanches can't happen with this next round of loading.

Snowpack Summary

Strong and variable winds in exposed treeline and alpine areas has resulted in reverse loading, sastrugi, surface crusts, and looming undermined cornices. Dribs and drabs of new snow over the past couple of days adds to the approximately 50cm of recent low density storm snow. Loose surface snow, storm slabs, and/or weak wind slabs are bonding poorly to a variety of old snow surfaces, including crusts, faceted snow, and wind slabs, from last week. Recent winds and precipitation patterns have created a highly variable somewhat upside-down upper snowpack. Storm and wind slabs have shown propensity to release mid-slope, propagate into low angled terrain, and step-down to deeper weaknesses.

Problems

Wind Slabs

An icon showing Wind Slabs
Recent variable winds have deposited fresh wind slabs in unusual places, but generally lurking below ridgecrests, behind terrain features and in gullies. Heavy loading is expected to cause large natural avalanches.

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

Elevations: Alpine, Treeline.

Likelihood

Very Likely

Expected Size

1 - 5

Persistent Slabs

An icon showing Persistent Slabs
Heavy loading is expected reinvigorate the mid-February persistent weakness. The potential for remote triggering, step down avalanches, and wide propagations makes this persistent slab problem particularly tricky to manage.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

3 - 8

Storm Slabs

An icon showing Storm Slabs
Any new snow is expected to initially bond poorly, and deeper weaknesses within and under recent storm snow are expected to be overloaded.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 5

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