Avalanche Forecast

Issued: Dec 5th, 2012 8:57AM

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

triley, Avalanche Canada

South Coast.

Summary

Confidence

Fair - Due to limited field observations for the entire period

Weather Forecast

Overnight and Thursday: Mostly cloudy with light precipitation overnight. Mostly dry with some sunny breaks during the day. Moderate westerly winds and temperatures near -10.0 in the alpine.Friday: Some light precipitation overnight. Sunny periods during the day with moderate west – southwest winds, gusty periods in the evening. Alpine temperatures continue to be about -10.0Saturday: Sunny periods with light winds and alpine temperatures about -7.0

Avalanche Summary

No new reports from the Coquihalla. The Duffey Lake area reports numerous natural cornice releases up to size 2.0, and one size 2.5 from a West aspect at 2150 metres. Suspect the sliding weak layer to be the late November surface hoar that is buried down about 70 cms.

Snowpack Summary

Another 36 cms in the past 24 hours brings recent snow fall amounts up to about 120 cms for the Coquihalla Pass area. Duffy Lake area has seen about 50-70 cm. Weaknesses linger within and under this storm snow. Of particular note is surface hoar buried late last week, which is likely well preserved and weak on sheltered open slopes treeline and below. The mid-pack seems to be well settled and strong, and possibly bridging deeper weaknesses. However, it wasn't too long ago when snowpack tests were producing moderate but sudden collapse results on the early November facet/crust combination near the base of the snowpack. Furthermore, favorable slab structure for step-down fractures can contribute to the persistence of this deep weakness.

Problems

Wind Slabs

Fresh wind slabs can be found well below ridge crests, behind terrain features and in cross-loaded gullies in any wind-exposed terrain. Expect these deep drifts to be very touchy.

Avoid freshly wind loaded features.>Travel on ridgetops to avoid wind slabs on slopes below.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

2 - 5

Storm Slabs

Weaknesses within and under the recent storm snow are susceptible to human and natural triggers and could easily produce avalanches large enough to bury a person.

Be alert to conditions that change with elevation.>Be cautious of sluffing in steep terrain.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 5

Persistent Slabs

An old facet/crust combination deep in the snowpack may wake up with heavy triggers, smaller avalanches stepping down, or triggering from thin-spots, particularly on slopes with smooth ground cover.

Be aware of thin areas that may propagate to deeper instabilites.>Be aware of the potential for full depth avalanches due to deeply buried weak layers.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Dec 6th, 2012 2:00PM