Avalanche Forecast

Issued: Nov 28th, 2012 9:27AM

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 Inland.

Summary

Confidence

Poor - Intensity of incoming weather is uncertain

Weather Forecast

A large low pressure system off the Gulf of Alaska will be bringing a very moist and active weather pattern over the next five days. Initially, the Northern sections may see cold arctic air being pushed in by a surface ridge of high pressure, then as a consistent moderate southwest flow sets up; it brings a series of systems which then the arctic air will start to retreat slowly from the Northwest regions. Expect strong outflow wind.Thursday/Fiday: FLVL’s surface, with a short lived AFL 100-1500 m, Thurs snow 8-15 cm, Fri snow 5-10 cm, ridgetop winds SE 30 km/hr, alpine temps -12 (inversion)Saturday: FLVL’s surface (no inversion), snow 7-10 cm, ridgetop winds E 15 km/hr, alpine temps -10.

Avalanche Summary

No new natural avalanches have been reported. Fresh wind slabs have been observed in exposed areas, but slope testing produced very few results.

Snowpack Summary

New storm slabs, and wind slabs will be forming over the next few days and instabilities are likely to exist. The new snow will add to the variable snow depths, and weaknesses that rest below. At treeline depths in the southern part of the region (west of Smithers) range between 70 – 125 cm, but highly variable with deep wind drifts and scoured slopes in exposed areas. A couple of notable weaknesses have been observed in the snowpack: first, a storm snow weakness (may also include small surface hoar) down 40-50cm. Second, a facet/crust combo that formed in early November is now down 40-75cm. This layer has produced moderate "drops" results in recent snowpack tests. Because this weakness is so close to the ground in most areas, associated avalanche activity will likely be limited to slopes with smooth ground cover (e.g. scree slopes, rock slabs, grassy areas, etc.) It will be important to keep tabs on this layer through the next storm cycle, and monitor its reaction to the additional load. Check out the recent forum posts here.

Problems

Wind Slabs

Natural avalanche activity is possible with heavy loading from snow and wind and human triggering is likely, especially on steep convex slopes. Expect to find wind slabs below ridgecrests, behind terrain features, and in cross-loaded gullies.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>Avoid lee and cross-loaded terrain near ridge crests.>

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

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Persistent Slabs

Basal facet/crust weaknesses are often 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.

Be aware of thin areas that may propagate to deeper instabilites.>Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 4

Valid until: Nov 29th, 2012 2:00PM