Avalanche Forecast

Issued: Mar 25th, 2013 10:14AM

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

swerner, Avalanche Canada

Northwest Inland.

Summary

Confidence

Fair - Due to limited field observations

Weather Forecast

The inland sections of the North Coast may only see high cloud and very little precipitation as the existing low diminishes. Tuesday: Light precipitation near 5 mm. Ridgetop winds will blow moderate from the South West. Alpine temperatures steady near -5.0 and freezing levels hovering around 1000 m in the afternoon.Wednesday/Thursday: Mainly dry conditions with lingering valley cloud. Ridgetop winds blowing light from the SouthWest. Alpine temperatures near -6.0 and freezing levels at 900 m in the afternoon.

Avalanche Summary

On Sunday, natural avalanche activity seemed to taper off. However, there was one report of natural icefall size 2.0. Natural cornice fall is expected through the forecast period with warmer afternoon temperatures and solar radiation. Over the past week skiers were remote triggering large destructive avalanches (size 2.5) from as far as 800m away. It has been an active period, with numerous avalanches reported to have failed on the March 9th layer. This layer is still a concern, but may trend to a low probability-high consequence scenario.

Snowpack Summary

Strong winds have redistributed storm snow on lee aspects creating stiff wind slabs. 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 trust steep north or east facing slopes at this time either.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, forming a melt-freeze crust overnight.

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 afar is possible.

Avoid large, steep alpine bowls.>Plan escape routes and identify safe zones before committing to your line.>Dig down to find and test weak layers before committing to a line.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 7

Wind Slabs

Strong SE winds have transported new new on lee slopes and behind terrain features. Wind slabs may be stiff, smooth and hollow sounding. Avoid freshly loaded areas.

Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.>Avoid cross loaded slopes at or above treeline.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 5

Cornices

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. Cornices will likely become weak if the sun is shining.

Give cornices a wide berth when travelling on or below ridges.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 6

Valid until: Mar 26th, 2013 2:00PM