Avalanche Forecast

Issued: Dec 1st, 2012 8:49AM

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

swerner, Avalanche Canada

Northwest Coastal.

Summary

Confidence

Poor - Timing, track, or intensity of incoming weather is uncertain on Tuesday

Weather Forecast

The recent weather pattern continues, with a very persistent deep low off the coast driving a moist, mild SW flow mostly over the southern parts of the province. In the North the arctic air will being to retreat on Sunday. Light accumulations are expected to continue accompanied by light-moderate SW winds. Seasonal normal temperatures will exist.Sunday: Fzlvlâ€™s 400 m, snow amounts 5-10 cm, ridgetop winds SE 15 km/hr, alpine temps -6.Monday: Fzlvlâ€™s 400 m, snow amounts near 5 cm, ridgetop winds SE 15 km/hr, alpine temps -6.Tuesday: Fzlvlâ€™s surface, snow amounts up to 20 cm, ridgetop winds E 30 km/hr, and alpine temps -8.

Avalanche Summary

On Thursday: a report of a skier triggered size 1.0 occurred on a E-SE aspect @ 1180 m, down 10-40 cm and 15 m wide, on a convex cross-loaded terrain feature. Explosive control performed in the region also triggered several size 1.0-1.5 slab avalanches, 25 cm deep, 30 m wide.

Snowpack Summary

Recent observations suggest that the alpine is fairly wind hammered from the recent steady, moderate SE winds. Hard slabs, storm, and wind slab instabilities exist at treeline and in the alpine.Â Hard slabs are harder to trigger, but may have larger consequences due to wider propagations. Storm and wind slabs may be touchy to rider triggers; especially on leeward slopes and behind terrain features where pockets of wind slab easily build. A couple recent test results done in the upper storm snow show an easy (RP) shear down 20-25 cm and a hard (RP) down 80 cm. The mid-pack is gaining strength and is well settled.Digging down deeper is the early November facet/crust layer. This crust sits near the base of the snowpack, and recent tests done in the Bear Pass area around 1100 m have shown this layer to be unreactive. Testing done in the Shames area on this interface have also shown no results, with moist snow below.Total snowpack depth is probably around 150-180 cm at treeline, and deeper but more variable in the alpine. The snowpack at below treeline elevations is reported to be strong.

Problems

Storm Slabs

New storm and wind slabs have formed; especially on lee slopes and behind ridges. Reverse loading patterns may exist, and pockets of wind slab could surprise you. Natural activity is possible with continued loading, and rider triggers are likely.

Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>Use ridges or ribs to avoid pockets of wind loaded snow.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

Basal facet/crust weaknesses are prone to remote triggering and step down avalanches, and typical trigger points include thin rocky areas. They may be difficult to trigger, but deep persistent slab avalanches are often very large and destructive.

Be aware of thin areas that may propagate to deeper instabilites.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Dec 2nd, 2012 2:00PM