Avalanche Forecast

Issued: Mar 5th, 2013 8:15AM

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

pmarshall, Avalanche Canada

South Coast.

Avalanche danger below treeline may be LOW in the Cascades where the surface rain crust extends up to higher elevations.

Summary

Confidence

Fair

Weather Forecast

Synopsis: A low pressure system will slide southeast and be replaced by a ridge of high pressure bringing more sunshine and mild temperatures for Thursday and Friday. Wednesday: Cloudy with a chance of flurries in the morning and sunny breaks in the afternoon. The freezing level is around 1200 m and winds are light from the southeast. Thursday: A mix of sun and cloud. The freezing level is steady around 1400 m and winds are light from the west-northwest. Friday: Mainly sunny. The freezing level should climb to 1600-1800 m during the day.

Avalanche Summary

Natural avalanche activity decreased on Sunday but there was one report of a size 2 skier triggered avalanche in the Duffey Lake area that resulted in injuries. Explosive control on the Duffey Lake road also produced several avalanches up to size 3 from northwest aspects. Most of these were suspected to have released on the late February surface hoar layer. There were no reports of new avalanches on Monday.

Snowpack Summary

Moderate ridge top winds have formed new wind slabs in exposed lee terrain. A dusting of new snow sits on 60-100 cm of settling storm snow or a rain crust below 1400 m in the north, and 1700 m in the south. Storm snow weaknesses have been gradually gaining strength over the past couple days. A weak layer of buried surface hoar (February 20th) and/or a crust sits at the base of the storm snow. This layer was the culprit in most of the large avalanches that occurred last weekend. Snowpack tests continue to show moderate "pops or drops" results and good potential for propagation. Triggering this layer is becoming more difficult, but I recommend avoiding any large slopes that did not release during the last cycle, especially when the sun pokes out later this week.

Problems

Persistent Slabs

60-120 cm of settling storm snow sits on a persistent weak layer (surface hoar or crust). Triggering this layer is becoming less likely but extra caution should be given on all slopes over 30 degrees that did not previously slide.

Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>Be wary of slopes that did not previously avalanche - even on low angle terrain.>Avoid shallow snowpack areas where triggering is more likely.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 7

Wind Slabs

Touchy wind slabs can be found on a variety of aspects and could be triggered by the weight of a person.

Use ridges or ribs to avoid pockets of wind loaded snow.>Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Valid until: Mar 6th, 2013 2:00PM