Avalanche Forecast

Issued: Dec 5th, 2012 8:56AM

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

swerner, Avalanche Canada

Northwest Coastal.

Summary

Confidence

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

Weather Forecast

Thursday: The region will be under the influence of a Westerly zonal flow. This will bring cooler temperatures, mainly cloudy skies and continuous light-moderate snow, alpine temps -9, ridgetop winds S 30km/hr. Friday through Saturday: A weak low pressure system moves into the region bringing moderate snow, ridgetop winds W 15 km/hr, and alpine temps near -10.

Avalanche Summary

Tuesday: Isolated natural size 2.0 avalanches from steep terrain features. Numerous size 2.0 explosive controlled avalanches 1400 m and above on North aspects , running within the new storm snow.

Snowpack Summary

Up to 60 cm of new storm snow, accompanied by strong NW-SE winds has fallen over the region in the past 4 days. Wind slabs continue to dominate the upper snowpack. The snow surface conditions in the alpine and at treeline 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.For more information and observations from the area, please check out the Regional Forum Posts.

Problems

Wind Slabs

Continuous outflow winds over the past 5 days has built wind slabs on E-NE aspects. Switching winds may build new wind slabs on opposite lee slopes and behind ridges. Natural activity is possible with continued loading, and rider triggers are likely.

Stay off recent wind loaded areas until the slope has had a chance to stabilize.>Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Deep 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 6th, 2012 2:00PM