Avalanche Forecast

Issued: Dec 23rd, 2011 9:13AM

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

Avalanche Canada pgoddard, Avalanche Canada

Summary

Confidence

Fair - Intensity of incoming weather is uncertain on Monday

Weather Forecast

Saturday: 5-10cm of snow with strong SW winds. Freezing level at valley bottom.Sunday: 5-10cm of snow with strong SW winds. Freezing level 1000m, lowering to valley bottom in the evening.Monday: Light to moderate snow with freezing levels remaining at valley bottom.Expect enhanced snowfall amounts on the western side of the range - quantities could be as much as doubled in some specific locations (and consequently higher than posted danger ratings should be anticipated).

Avalanche Summary

No new avalanches have been reported since Wednesday. It's a big area, however, and we receive limited reports. Earlier in the week, a natural avalanche cycle was observed in the South Cariboos, mostly on north aspects in the alpine. Several rider-triggered avalanches occurred, with the mid-December hoar/facet/crust interface causing most concern. With new wind-slabs building over these known weaknesses, further avalanche activity remains a distinct possibility.

Snowpack Summary

Recent storm snow continues to be redistributed by strong southwest winds. Wind slabs with the potential to propagate widely exist in the alpine, particularly on north through east aspects. At treeline, pockets of wind slab also exist. A surface hoar/facet/crust interface is buried anywhere from 30- 80cm deep and has recently proven itself to be variable in its distribution, with concerning (sudden planar) results in snowpack tests and rider-triggered avalanches in some places and little results in other places. This means the problem is somewhat spotty, but could be lurking round the corner - and have huge consequences if triggered.A resistant-type shear about 30cm down within the recent storm snow also exists. A sun crust also exists in the alpine on steep south and west aspects. The mid-pack is generally strong and well settled. Over the Christmas weekend, a high level of training will be required to effectively manage the risks posed by slabs sitting over the buried interface from mid-December. Avalanches could be triggered by you if you venture into the wrong terrain - the most likely areas are steep, convex rolls, sheltered slopes around treeline, big open alpine terrain and thin-spot trigger points. They could also be triggered naturally as incoming weather adds more snow and wind-loading to the recipe. To be able to travel safely, you'll need the skills to recognise whether snowpack weaknesses exist on the slopes you are considering travelling on, strong group management skills and a good measure of judgement and discipline.

Problems

Wind Slabs

An icon showing Wind Slabs
Wind slabs exist on lee and cross-loaded features. Wind slabs could fail on persistent weak layers with the potential for large avalanches.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 5

Persistent Slabs

An icon showing Persistent Slabs
A cohesive slab exists above the early December buried surface hoar/facet interface in some locations. This weakness may produce wide propagations. Deeper persistent weak layers also exist.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 6

Valid until: Dec 24th, 2011 8:00AM

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