Avalanche Forecast

Issued: Dec 15th, 2012 8:08AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Wind Slabs and Storm Slabs.

pmarshall, Avalanche Canada

South Coast.

Summary

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. forecaster@avalanche.ca

Problems

Wind Slabs

Weak wind slabs may be encountered below ridge crests, behind terrain features and in cross-loaded gullies.

Be cautious as you transition into wind affected terrain.>Use ridges or ribs to avoid pockets of wind loaded snow.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Storm Slabs

Weaknesses may exist within or under the new storm snow and may be triggered easily by the weight of a person or snowmobile.

Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>Choose conservative lines and watch for clues of instability.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 4

Valid until: Dec 16th, 2012 2:00PM