Avalanche Forecast

Issued: Mar 24th, 2013 10:13AM

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

swerner, Avalanche Canada

Northwest Inland.

The March 9th persistent weakness is sensitive to human triggering and has produced frighteningly large avalanches. Continue to stay conservative in your approach to the mountains.

Summary

Confidence

Fair - Due to limited field observations

Weather Forecast

Monday: As a Pacific cold front tracks eastward, the region will see light precipitation amounts accompanied by moderate SW winds. Alpine temperatures will be steady around -6.0 with freezing levels around 1000 m.Tuesday/Wednesday: Will see mainly sunny skies with few clouds. Alpine temperatures will be near -7.0, freezing levels will hover around 900 m in the afternoon then falling back to valley bottom overnight. Ridgetop winds will be light from the NW on Tuesday, then blowing light form the SW on Wednesday.

Avalanche Summary

No new natural avalanche activity has been reported. Over the past several days skiers were remote triggering large destructive avalanches (size 2.5) from as far as 800m away. It has been an active recent period, with numerous avalanches reported to have failed on the March 9th layer over the past week.

Snowpack Summary

Anywhere from 35 - 65 cm of recent snow sits on a variety of old snow surfaces, including crusts, previous wind slabs and a buried surface hoar layer (March 9th). The March 9th surface hoar layer has been very touchy in many areas and many large avalanches have released on it. Recent snowpack tests are showing very easy shears which means this layer should not yet be trusted. The distribution of the surface hoar is variable and it may not exist, or be reactive, in every drainage. Where it does exist, it appears to be present at all elevations, but is likely to pose the biggest threat in the alpine. Recent reports indicate it has been more reactive on south through west aspects, but I wouldn't necessarily trust steep north or east facing slopes at this time either. I suspect cornices have become well-developed and could easily become unstable during periods of warm weather or on slopes receiving direct sun. Most snow surfaces exist on solar aspects up to 2300 m. The mid snowpack is generally well settled and strong.

Problems

Persistent Slabs

A 30 - 60cm slab sits on the March 09 surface hoar/crust combo. The distribution of this layer seems to be variable. However if triggered, a large destructive avalanche will occur with consequences. Remote triggering from great distances is possible.

Avoid large alpine bowls if you have an uncertainties.>Choose regroup spots that are out of avalanche terrain.>Dig down to find and test weak layers before committing to a line.>Plan escape routes and identify safe zones before committing to your line.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 7

Wind Slabs

Large well developed cornices loom over many slopes. It's likely that cornice failure will initiate large avalanches failing on the March 09 persistent weak layer. Wind slabs also exist on lee slopes and behind terrain features.

Avoid freshly wind loaded features.>Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>Pay attention to overhead hazards like cornices.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 5

Valid until: Mar 25th, 2013 2:00PM