Avalanche Forecast

Issued: Feb 22nd, 2012 9:42AM

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

swerner, Avalanche Canada

South Coast.

A touchy weak layer, forecast snow and strong winds will likely produce dangerous avalanche conditions.

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain on Friday

Weather Forecast

A ridge of high pressure builds off the coast bringing mainly dry, cool conditions with possible scattered flurries on Thursday. Ridgetop winds will blow 60-80km/her from the West. Freezing levels at valley bottom. On Friday a low pressure system arrives off the coast bringing moderate precipitation amounts. Snow amounts 15-20cm. Freezing levels may rise to 900m. Saturday snow amounts light in the morning, may start to taper off mid-day.

Avalanche Summary

Coquilhalla Area: Several natural size 2-2.5 slab avalanches occurred on West aspects. Crown depths being 50-100cm, and running 100m in distance. Skier triggered size 1.5 failed on the above mentioned graupel layer, @1650m on an East aspect, running 100m in length.

Snowpack Summary

Over the past few days 20-30 cm of new snow fell over the Duffy Lake area. The Coquihalla has seen up to 50 cm. This new snow has buried a variety of old snow surfaces that formed during a sunny dry spell over the past 2 weeks. The old surfaces include: melt-freeze crusts on all aspects below 1700m and on steep solar aspects higher up, surface hoar (feather like crystals), old wind slabs, and facets (sugary crystals), which exist on north aspects as well as around crusts. The surface hoar seems to be most prominent in sheltered treeline locations and below, and most likely found in the north and central parts of the region. We may see these buried weak layers become naturally reactive with forecast snow and wind, and likely susceptible to rider triggers. If the sun starts to shine through on Thursday afternoon, I'd be suspect of a weakening snowpack on solar aspects. Generally below this sits a well settled snowpack, with treeline snowpack depths near 250cm. Test results on the Duffy today shows RB4 down 35cm on 3mm Surface Hoar, sudden planar results. For insight on incremental loading, and the "Tipping Point" check out our latest Forecaster's Blog. To view recent photos of this buried surface hoar in the Coquihalla area please click this link:https://avalanche.ca/cac/library/avalanche-image-galleries/avalanches2012

Problems

Wind Slabs

Strong winds will blow around the new snow creating wind slabs on lee slopes. As these slabs build, they will increase the load on buried weak layers.

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 5

Persistent Slabs

Additional snow will continue to form storm slabs through the forecast period. Amounts look to be higher in the Coquihalla area, forming storm slabs faster then the Duffy. These sit on a variety of buried weak layers, and likely to reach threshold.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 5

Valid until: Feb 23rd, 2012 8:00AM