Avalanche Forecast

Issued: Dec 19th, 2014 8:41AM

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

triley, Avalanche Canada

South Coast.

Avalanche danger is increasing as the storm slab continues to develop.

Summary

Confidence

Poor - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

Light snow (3-8 cm) overnight combined with moderate to strong Southwest winds and freezing levels at or below 1000 metres. Another 5-10 cm of snow during the day on Saturday combined with very strong Southwest winds and freezing levels rising up above 1500 metres in the afternoon. Very strong Southwest winds and another 8-12 cm of new snow by Sunday morning. Winds decreasing to strong Southwest with 3-5 cm of new snow and freezing levels climbing back up to about 1600 metres during the day on Sunday. Monday should be drier, with less wind and dropping freezing levels.

Avalanche Summary

No new reports of avalanches. Expect new storm slab avalanches to increase as the new storm develops.

Snowpack Summary

The new storm is expected to develop a storm slab above the mix of old surface forms that include hard crusts, near surface facets, and surface hoar. In the Coquihalla there is 65-80 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 40 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

Forecast new snow and strong winds may develop windslabs in the alpine and at treeline. The storm snow is expected to consolidate into a slab allowing for longer propagations resulting in larger avalanches.

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 load of new storm snow is expected to increase the likelihood of avalanches releasing on the deeply buried weak layers. Avalanches that release on a deeply buried weak layer may be large and destructive.

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 20th, 2014 2:00PM