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Avalanche Forecast

Archived

Dec 15th, 2012–Dec 16th, 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 and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
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.

Regions

South Coast.

Confidence

Fair - Track of incoming weather is uncertain

Weather Forecast

Synopsis: A strong frontal system is forecast to reach the South Coast late on Sunday bringing moderate to heavy snow and strong winds. Conditions should be unsettled in the wake of the system with flurries and occasional sunny breaks. Sunday: Periods of snow, heavier in the evening and overnight. 25-40 cm in the south, and 15-25 cm in the north (by Monday morning). Winds increasing to strong from the SW with the arrival of the system. Freezing level at valley bottom. Monday: Snow easing to flurries and possible sunny breaks. Around 5 cm. Freezing level at valley bottom. Tuesday: Cloudy with flurries. Freezing level at valley bottom.

Avalanche Summary

There were a few reports of small natural and human triggered loose snow avalanches, and isolated thin wind slabs immediately lee of ridge crests late last week. Previous reports include evidence of large avalanches, including one from Mt Joffre at 2000m and the east face of Cayoosh Mountain in the Duffy Lake area last weekend (check out Wayne Flann's Avalanche Blog for a photo of the Cayoosh avalanche).

Snowpack Summary

Several weaknesses may exist within and under the new storm snow, including one or two surface hoar layers and a sun crust. Moderate to strong southwesterly winds have probably redistributed low density snow into soft wind slabs in exposed lee terrain. The late November surface hoar is down 70-90 cm but produces inconsistent results with snowpack testing. A well settled and rounding mid-pack is overlaying the early November crust, which continues to give occasional sudden planer compression test result in the overlying facets. Meanwhile in the Coquihalla area, recent reports suggest an overall well settled "right side up" (progressively more dense with depth) snowpack. The early November crust has not been found in the Coquihalla, although we don't have any reports from the high alpine. Conditions may be quite different in the Northern part of this region, please email us your observations if you are out in the field. [email protected]

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.