Avalanche Forecast

Issued: Dec 6th, 2012 9:25AM

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

triley, Avalanche Canada

South Coast.

The possibility of very large avalanches failing on the deeply buried crust is keeping the Alpine Danger elevated. I don't think we should trust big alpine slopes yet! Check out the forecast details for more info.

Summary

Confidence

Fair - Due to variable snowpack conditions on Friday

Weather Forecast

Overnight and Friday: Light precipitation overnight bringing 3-5 mm that should fall as snow above 800 metres elevation by late morning. Winds light westerly and alpine temperatures about -7.0Saturday:Light precipitation under cloudy skies, with light westerly winds and -10.0 in the alpine.Sunday: A Pacific frontal system is expected to move onto the coast during the day on Sunday. Expect a strong Southwest flow with moderate to heavy precipitation amounts.

Avalanche Summary

Explosive control in the Duffey Lake area resulted in avalanches up to size 2.5 that were 30-40 cms deep.

Snowpack Summary

16 cms in the past 24 hours and 52 cms in the past 48 hours brings recent snow fall amounts up to about 135 cms for the Coquihalla Pass area. Duffy Lake area has seen about 60-80 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

The recent storm has developed wind slabs in the alpine and at treeline that may be covered by 20-30 cms of new snow.

Avoid freshly wind loaded features.>Use ridges or ribs to avoid pockets of wind loaded snow.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 4

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 7

Valid until: Dec 7th, 2012 2:00PM