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Avalanche Forecast

Archived

Dec 19th, 2012–Dec 20th, 2012

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

Regions

South Columbia.

Confidence

Good

Weather Forecast

Wednesday night:  Strong to Extreme SW winds at ridgetop.Thursday: Strong to Extreme SW winds at ridgetop. 1500m temp -5. Moderate to heavy snow totaling 5 - 15cm with greatest accumulations in the south. Friday: Moderate to Strong southerly winds. 1500m temp -5.  Occasional flurries.Saturday:  Light West Winds.  Treeline temp -1. Light snow.

Avalanche Summary

There was a widespread cycle of small natural and skier triggered soft slab and loose snow avalanches on Monday. Soft new cornices were also falling off and triggering soft slabs up to size 2. Some larger (size 2-3) naturally triggered slabs were observed to the north of the region. Explosives triggered a size 2 soft slab which stepped down to the late November surface hoar layer in a steep rocky area in the Selkirks on Sunday.

Snowpack Summary

More than 120 cm of snow has accumulated this week in some areas. Various storm snow instabilities have been observed. In areas affected by recent SW to SE winds, new wind slabs and touchy cornices exist at alpine and treeline elevations. In areas sheltered from the wind, the new snow is sluffing fast and far, with enough ?push? to get you into trouble. The mid-pack is reported to be settling well. The late November surface hoar, down 100-160 cm (between 1500 and 2000 m), is producing moderate to no results in snowpack tests, with isolated sudden results. The early November crust, near the base of the snowpack, has produced occasional sudden results in snowpack tests. Professionals are still cautious about these lingering persistent slab problems, but the likelihood of triggering is low. Be wary of steep complex terrain with a shallow snowpack, where triggering a persistent weakness is more likely.

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.