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Avalanche Forecast

Archived

Nov 28th, 2012–Nov 29th, 2012

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Northwest Inland.

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

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.