Avalanche Forecast

Issued: Dec 21st, 2014 7:54AM

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

triley, Avalanche Canada

South Coast.

There may be a lot of variability between the North and South areas of this region. Time to dig down and find out what the snowpack looks like in your area, and then share your observations with us!

Summary

Confidence

Poor - Due to the number of field observations

Weather Forecast

Flurries or light snow overnight combined with strong Westerly winds and dropping freezing levels. Drier and cooler on Monday with periods of broken skies with light Westerly winds. The next storm should move into the region sometime early on Tuesday morning and bring 5-10 cm during the day with strong Southwest winds. The storm should continue overnight and into Wednesday morning, but at this time the snowfall amounts look very light.

Avalanche Summary

Soft slab avalanches were reported during the storm from alpine North aspects up to size 1.5 on Saturday. I suspect that storm slab avalanches continued on Sunday with the additional 20-25 cm of new snow combined with strong winds.

Snowpack Summary

The new storm slab may be 40-50 cm thick in The Coquihalla and is reported to be bonding well to the December 11th crust. In the Coquihalla there is 70-100 cm of snow on the ground above 1600 metres elevation, and below threshold for avalanches below 1500 metres. The recent surface hoar has been reported to have been mostly blown away by the Northeast wind before this new storm. In the North of the region it sounds like the recent surface hoar is 2-4 mm at treeline and up to 30 mm near open creeks below treeline. The knife hard December melt-freeze crust extends up to about 2100 metres and then tapers off to nothing by 2300 metres. The new storm slab may be up to 70 cm in the North of the region, and it may not be bonding well to the old crust/ surface hoar combination. The November crust is deeply buried and may become easier to trigger in isolated areas if the load from the storm slab overcomes the bond at the crust interface.

Problems

Storm Slabs

The recent storm slab is expected to take a few days to settle and bond to the old surfaces. Some deep pockets of windslab may exist in the alpine and at treeline on terrain that is in the lee of Southwest winds.

Avoid freshly wind loaded features.>Avoid open slopes and convex rolls at treeline where buried surface hoar may be preserved.>Give cornices a wide berth when travelling on or below ridges.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Deep Persistent Slabs

The increasing load of new storm snow may increase the likelihood of triggering the deeply buried weak crust layer.

Be aware of thin areas that may propogate to deeper instabilites.>Avoid convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

3 - 5

Valid until: Dec 22nd, 2014 2:00PM