Avalanche Forecast

Issued: Nov 30th, 2012 8:47AM

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

swerner, Avalanche Canada

Northwest Coastal.

Summary

Confidence

Poor - Due to limited field observations for the entire period

Weather Forecast

The weather pattern continues with generally cloudy skies, light amounts of precipitation, light winds and cool air. The arctic air mass that has been stationary over the Northern part of the province will slowly start to retreat Sunday afternoon bringing temperatures back to seasonal norms, and the strong outflows will diminish. Saturday: FLVL’s 200 m, snow amounts 5 cm, ridgetop winds SE 20 km/hr, alpine temps near -8.Sunday: FLVL’s 400m, snow amounts 5-10 cm, ridgetop winds SE 15 km/hr, and alpine temps - 7.Monday: FLVL’s surface, ridgetop winds SE 15 km/hr, alpine temps -10.

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

New storm slabs and wind slabs instabilities exist at treeline and alpine locations. They 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 generally gaining strength and 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 proved this layer to be unreactive. Testing done in the Shames area on this interface also showed 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.>Avoid travelling in areas that have been reverse loaded by winds.>Be alert to conditions that change with elevation.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very 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 1st, 2012 2:00PM