Avalanche Forecast

Issued: Mar 8th, 2012 8:55AM

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

ccampbell, Avalanche Canada

South Coast.

Summary

Confidence

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

Weather Forecast

Friday: Moderate to heavy snow and strong southwesterly winds with 20-30cm possible by the end of the day. Freezing levels are expected to drop to 1000m. Saturday and Sunday: Continued light to moderate snowfall and strong south to southwest winds with freezing levels remaining in the 500-1000m range.

Avalanche Summary

Tuesday's reports from Duffey Lake and Chilcotin areas suggest that a persistent facet/crust weakness is very touchy in treeline gullies and below treeline cutblocks. Several Size 2.0-2.5 persistent slabs, including multiple sympathetic releases, were skier-triggered in treeline features (gullies) and below treeline cutblocks. 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, widespread surface crusts, and looming undermined cornices. In the Duffey Lake and Chilcotin regions south aspects are described as spooky with a very hollow feeling with a couple of different poorly-bonded crusts in the upper snowpack. The lower weakness, down 60-80cm at treeline and over a metre at higher elevations, is not only particularly touchy on south aspects, but on all aspects at lower treeline and below, where there is also an associated crust. Lingering pockets of this mid-February surface hoar and/or facets elsewhere (steep easterly aspects, sheltered concave slopes, and protected valleys, for instance) necessitates continued "heads-up" travel. Meanwhile in the Cascades, 70-100cm of recent storm snow combined with five straight days of sustained extreme winds has created a highly unstable wind and storm slab problem that will probably take a few days to settle and strengthen.

Problems

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: All elevations.

Likelihood

Likely - Very Likely

Expected Size

3 - 7

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

2 - 5

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

Likely

Expected Size

1 - 5

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