Avalanche Forecast

Issued: Mar 26th, 2013 9:56AM

The alpine rating is considerable, the treeline rating is moderate, 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

High pressure and an offshore flow develops today over the North Coast. Sunny skies and spring-like conditions will persist through to Friday. The next low pressure system is expected to arrive Saturday. Wednesday: Mix of sun and cloud. Very light precipitation expected. Alpine temperatures near -7.0. Freezing levels rising to 1200 m in the afternoon. Ridgetop winds will blow moderate from the West. Thursday/Friday: Sunny with some mid-high cloud cover. Alpine temperatures near -9.0. Freezing levels around 1400 m. Ridgetop winds blowing light from the SW.

Avalanche Summary

On Monday, numerous loose wet avalanches occurred from steep rocky terrain features.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.

Snowpack Summary

Northern areas of the region have experienced strong winds that 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).Last week, the March 9th surface hoar layer has been touchy in many areas and many large avalanches have released on it. Currently, this layer seems to be less reactive, but is still a concern (low probability-high consequence) . Recent snowpack tests are showing hard, resistent shears. This layer may be healing in some places, but I would remain conservative and continue to dig and test before diving into my line. 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. Cornices have become well-developed and could easily become unstable during periods of warm weather or direct solar radiation. 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 may occur with consequences. Remote triggering from afar is possible

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

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.

Avoid freshly wind loaded features.>Use extra caution on cross loaded slopes at or above treeline.>Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 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 - Likely

Expected Size

1 - 6

Valid until: Mar 27th, 2013 2:00PM