Avalanche Forecast

Issued: Mar 7th, 2012 9:43AM

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

Avalanche Canada ccampbell, Avalanche Canada

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain for the entire period

Weather Forecast

Thursday: Increasing clouds throughout the day and moderate snowfall starting in the evening. Light winds increasing to strong southeasterlies with the onset of the storm. Freezing levels rising as high as 2000m, or higher in southern areas, but dropping in the evening. Friday: Heavy snow and strong southwesterly winds tapering off in the morning with 30-40cm total possible by the end of the day. Freezing levels are expected to drop to 700m. Saturday: Continued moderate precipitation and strong winds with freezing levels remaining in the 500-700m range.

Avalanche Summary

We received an initial report of an avalanche fatality in the southern Pemberton Icecap 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.

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 propagate in 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. Cornices are expected to weaken with warm temperatures and could trigger large wind slabs 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
Touchy weaknesses within and under the recent storm snow are expected to become more reactive with sun-exposure. Cohesionless low-density snow overlying a crust can produce very large loose-snow avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 6

Persistent Slabs

An icon showing Persistent Slabs
Warming temperatures combined with the potential for cornice triggers, remote triggering, step down avalanches, and wide propagations makes this persistent slab problem particularly tricky to manage.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 6

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