Avalanche Forecast

Issued: Dec 4th, 2012 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.

swerner, Avalanche Canada

Northwest Coastal.

Summary

Confidence

Poor - Due to limited field observations

Weather Forecast

An upper level trough will influence an onshore flow with several embedded systems. These systems will bring light-moderate amounts of precipitation. Winds will generally stay light and freezing levels will remain in valley bottoms through the forecast period.Wednesday: Snow amounts 10-15 cm, ridgetop winds SW 25 km/hr, alpine temps near -8.Thursday: Snow amounts 5-10 cm, ridgetop winds SW 20 km/hr, alpine temps near -10.Friday: Snow amounts 8-15 cm, ridgetop winds SW 10 km/hr, alpine temps near -10.

Avalanche Summary

On Monday a size 3 natural icefall avalanche was reported. Several natural sluffs size 1-1.5 initiated from steep terrain in below treeline elevations. Explosive avalanche control work also saw size 1-2 slab avalanches from North aspects, all failing in the recent storm snow. On Sunday in the Shames area, a fairly large (no size was listed) natural avalanche had was seen on a North aspect initiating from the alpine just below the ridgeline. A couple skier triggered size 1.5 slab avalanches were reported from the same group skiing down from the Dome. The slab initiated as the second skier made a turn over a convex slope. The slab was 20-40 cm deep, 20-30 m wide and ran approx. 50 m down slope. For more information and observations from the area, please check out the Regional Forum Posts.

Snowpack Summary

Up to 50 cm of new storm snow, accompanied by strong NW-SE winds has fallen over the region in the past 3 days. Wind slabs continue to dominate the upper snowpack. The snow surface conditions are variable with hard slabs, wind slabs and areas that are scoured. 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 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 above 1000 m is 150-200 cm deep. Below 1000 m the snowpack shows a sharp transition from 100 cm dropping to 50 cm, and is generally below threshold.

Problems

Wind Slabs

Wind slabs have formed; especially on lee slopes and behind ridges. Natural activity is possible with continued loading, and rider triggers are likely.

Avoid lee and cross-loaded terrain near ridge crests.>Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>

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

Elevations: All elevations.

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 5th, 2012 2:00PM