Avalanche Forecast

Issued: Mar 17th, 2013 10:39AM

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

jfloyer, Avalanche Canada

Northwest Inland.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

Synopsis: Northwest flow gives way to a frontal system that barely brushes the region on Tuesday night/Wednesday.Monday: Chance of flurries, with significant breaks in the cloud giving daytime warming. Afternoon freezing level around 500 m. Winds light northwesterly.Tuesday: Flurries late in the day. Freezing level 500 m. Southerly ridgetop winds increasing to around 50 km/h.Wednesday: Around 5 cm new snow. Freezing level 500 m. Winds light southeasterly.

Avalanche Summary

On Saturday, a size 2 avalanche was triggered remotely on a south aspect at 1800 m. This avalanche ran on the new snow/crust interface about 40 cm below the surface. On Friday, a size 2 remote-triggered avalanche was reported from a west aspect at 1450 m, likely failing on the March 9th surface hoar layer down around 50 cm. Another human-triggered avalanche was reported on Friday from a north aspect slope.

Snowpack Summary

20-40 cm of recent storm snow rests on a variety of old snow surfaces, including crusts, previous wind slabs and surface hoar (buried March 9th). Warmer temperatures and recent winds have now set this new snow into a reactive slab. The March 9th surface hoar layer is reported to be very touchy and appears to exist at all elevations and on a variety of aspects. I suspect cornices have become well-developed and could easily become unstable with daytime heating. The mid snowpack is generally well settled and strong.

Problems

Storm Slabs

Recent new snow has consolidated into a slab and is reacting to human triggers. The primary weak layer comprises surface hoar and appears to be touchy.

Choose conservative lines and watch for clues of instability.>Avoid open slopes and convex rolls where buried surface hoar may be preserved.>Avoid freshly wind loaded features.>Choose well supported terrain without convexities.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 5

Cornices

Cornices are well developed. They are likely to be most sensitive when exposed to daytime heating or solar radiation.

Do not travel on slopes that are exposed to cornices overhead.>Stay well to the windward side of corniced ridges.>

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

2 - 5

Valid until: Mar 18th, 2013 2:00PM