Avalanche Forecast

Issued: Mar 4th, 2013 8:09AM

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

pmarshall, Avalanche Canada

South Coast.

Summary

Confidence

Fair

Weather Forecast

Synopsis: A weak weather system will bring more cloud and light precipitation to the South Coast for Tuesday and Wednesday. A ridge of high pressure should build in for Thursday and Friday bringing mainly sunny skies. Tuesday: Increasing cloud with light precipitation (2-4 cm). The freezing level will rise to around 1100 m during the day. Winds are light from the southeast. Wednesday: Cloudy with light precipitation (4-8 cm). 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.

Avalanche Summary

A widespread natural avalanche cycle to size 3.5 occurred on Friday and Saturday. Numerous large slabs failed on a surface hoar/crust weakness, many of which took out mature forest. Natural avalanche activity decreased on Sunday but explosive control on the Duffey Lake road 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.

Snowpack Summary

The recent storm delivered 60-70 mm of precipitation, which fell with warming temperatures, dropping rain below about 1600-1800 m. A subsequent drop in temperature has left a supportive frozen crust below treeline. Strong south to south-westerly winds during the storm created touchy wind slabs on lee terrain. A weak layer of buried surface hoar (February 20th) and/or a crust was overloaded during the storm, creating a widespread avalanche cycle. The lower snowpack is well settled.

Problems

Wind Slabs

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

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

80-120 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.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>Avoid paths that have not avalanched recently.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 7

Valid until: Mar 5th, 2013 2:00PM