Avalanche Forecast

Issued: Mar 20th, 2013 9:37AM

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

Peter, Avalanche Canada

South Coast.

Summary

Confidence

Fair

Weather Forecast

Synopsis: Cooler and unsettled conditions are expected for Thursday and Friday. A ridge of high pressure should start to develop on Friday resulting in drier and sunnier weather. Thursday: Mainly cloudy with a chance of flurries. The freezing level drops to around 400 m overnight and winds are moderate from the northwest. Friday and Saturday: A mix of sun and cloud. The freezing level drops to near sea level overnight and rises to 800 m during the day. Winds are light to moderate from the north-northwest.

Avalanche Summary

There is one new report of a size 1.5 skier triggered slab avalanche from the South Chilcotins on Tuesday. This avalanche occurred on a steep north aspect in the alpine and was triggered mid-slope. On Monday, a cornice fall triggered a size 3 slab avalanche on a NE aspect with a crown depth up to 100 cm. There is limited information on an accidentally triggered slab avalanche on Sunday in the Duffey Lake area that resulted in 2 people being buried.

Snowpack Summary

Freezing levels climbed to 1700-1800 m with the system on Wednesday, resulting in moist or wet snow below treeline. Recent snowfall amounts vary significantly throughout the region. In the Coquihalla area, 10-15cm of dense new snow sits on a melt-freeze crust or up to 90 cm of previous storm snow. At the base of the old storm snow is another melt-freeze crust buried around a week ago. Further to the north (Duffey Lake) there is 10-15 cm of new snow sitting on a sun crust, wind slab, or settling storm snow. A buried surface hoar layer can be found down 50-70 cm and may be associated with a sun crust on southerly aspects at treeline. For all areas, expect extensive wind slabs and cornices in the alpine.

Problems

Wind Slabs

New wind slabs are likely in exposed lee terrain and cross-loaded gully features. A wind slab avalanche could trigger deeper instabilities lower down on the slope, creating a very large avalanche.

Be cautious as you transition into wind affected terrain.>Highmark or enter your line well below ridge crests to avoid wind loaded pillows.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

A buried crust and/or surface hoar layer, now down 60-80 cm, could be triggered in sheltered areas near treeline. Avalanches stepping down to this layer could be very large and destructive.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>Choose well supported terrain without convexities.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 6

Cornices

Cornices are reported to be large and may become unstable with continued growth, mild temperatures and sunny periods.

Give cornices a wide berth when travelling on or below ridges.>

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

3 - 6

Valid until: Mar 21st, 2013 2:00PM