Avalanche Forecast

Issued: Dec 3rd, 2012 9:32AM

The alpine rating is high, 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

Weather Forecast

A broad upper trough remains just offshore while a cooler, unstable onshore westerly flow has strengthened. A multitude of systems will bring light –moderate precipitation, and strong SW winds. The region returns to normal seasonal temperatures, as the arctic air retreats.Tuesday: Freezing levels near 500 m, snow amounts 15-25 cm, ridgetop winds SW 50-70 km/hr, alpine temps -7.Wednesday: Freezing levels near 500 m, snow amounts 2-5 cm, ridgetop winds W 30 km/hr, alpin temps -9.Thursday: Freezing levels at the surface, snow amounts 5-10 cm, ridgetop winds SW 20 km/hr, alpine temps -11.

Avalanche Summary

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

Recent observations suggest that the alpine is fairly wind hammered from the steady, moderate SE winds. Hard slabs, storm, and wind slab instabilities exist at treeline and in the alpine. 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 is around 150-180 cm at treeline, and deeper but more variable in the alpine. The snowpack at below treeline elevations is near 100 cm deep, and reported to be strong.

Problems

Storm Slabs

New storm and wind slabs have formed; especially on lee slopes and behind ridges. Natural activity is likely with continued loading, and rider triggers are very likely.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 5

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 4th, 2012 2:00PM