Avalanche Forecast

Issued: Dec 7th, 2012 9:37AM

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

mbender, Avalanche Canada

Northwest Coastal.

Summary

Confidence

Poor - Due to limited field observations for the entire period

Weather Forecast

Saturday: The effects of a weak ridge of high pressure will be brief. Generally broken skies with little to no precipitation for most of the day with a warm front pushing in for the late afternoon. Light to moderate amounts of snow are expected for the overnight period into Sunday. Winds northwest 20 km/h for the daytime period changing to west 30-50km/h in the late afternoon. Alpine temperatures -8. Sunday: Moderate to heavy precipitation throughout the day with strong northwesterly winds. Alpine temperatures -3 degrees. Monday: Continued moderate precipitation with southwesterly winds 30km/h. Freezing levels expected at 800m with alpine temperatures -4 degrees.

Avalanche Summary

Explosives testing north of the Stewart region indicate avalanches running to size 2.5 in north facing terrain. These were isolated to the most recent storm snow. Any recent natural activity has been reported to size 1.5 and is also isolated to the recent storm snow.

Snowpack Summary

Up to 70 cm of new storm snow has fallen over the region in the past 5 days. This has been accompanied by strong winds from a wide variety of directions. Wind slabs continue to dominate the upper snowpack. Alpine and treeline surface snow conditions are variable with buried wind slabs, newly formed wind slabs and areas that are heavily scoured. Recent test results done in the upper storm snow show an easy resistant shear down 30-35 cm and a hard resistant down 80 cm. The mid-pack is gaining strength and is well settled.A November facet/crust layer can be found near the base of the snowpack. Tests done earlier in the week 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. We do not have much recent information on this facet/crust interface, so it would be worth digging down yourself to test for its existence and reactivity.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

Winds shifting in direction over the past 5 days have created windslabs on a variety of aspects.

Be cautious as you transition into wind affected terrain.>Use ridges or ribs to avoid pockets of wind loaded snow.>Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 4

Deep Persistent Slabs

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

Carefully evaluate big terrain features by digging and testing on adjacent, safe slopes.>Be aware of thin areas that may propagate to deeper instabilites.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

2 - 6

Valid until: Dec 8th, 2012 2:00PM