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Avalanche Forecast

Archived

Jan 12th, 2012–Jan 13th, 2012

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

Regions

South Columbia.

Confidence

Fair - Intensity of incoming weather is uncertain on Saturday

Weather Forecast

Friday: Cloudy with isolated light flurries, freezing levels in valley bottoms, and moderate to strong westerly winds. Saturday: 5-15cm of accumulation expected with freezing levels remaining in valley bottoms, and strong southwesterly winds. Sunday: Another 5-15cm possible with light to moderate southwesterly winds, and freezing levels in valley bottoms.

Avalanche Summary

Recent observations include a few natural and human-triggered small wind slab avalanches up to 40cm thick in lee and cross-loaded terrain. A strong wind-event on Tuesday triggered several Size 2-3 slab avalanches up to 50cm thick in steep north through west facing alpine terrain.

Snowpack Summary

Recent light amounts dry snow has maintained the snow supply for fresh wind slab development and cornice growth. Surface condition in wind-exposed areas is highly variable with scoured areas, sastrugi, and pockets of fresh hard and soft wind slabs. Recent strong winds have created high variability in treeline and alpine areas, with shallow faceted scoured areas, thick wind slabs, and thin trigger points. A weak graupel and/or stellar layer down 25-30cm appears to have been the culprit in recent wind slab avalanche activity. Avalanche professionals are gaining confidence in the mid-December persistent weakness, now down 90-170cm, but concern remains for heavy triggers, such as cornice drops, on steep unsupported slopes. When this persistent weaknesses is combined with weak wind slabs, thin trigger points, and other weaknesses within and under the recent storm snow and at the base of shallow snowpack areas, the result is a highly variable snowpack with the potential for step-down deep slab avalanches.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.