Avalanche Forecast

Issued: Dec 7th, 2012 9:20AM

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

triley, Avalanche Canada

Sea To Sky.

Summary

Confidence

Fair - Due to variable snowpack conditions on Saturday

Weather Forecast

Overnight and Saturday: A ridge of High pressure will build over the North Coast tonight and then move down onto the South Coast during the morning. Light snow is expected to bring a couple of cms to the region during the evening. Moderate Northwesterly winds and cooling temperatures (-12.0 in the alpine) are forecast by morning. Broken skies in the morning, with some sunny periods in the afternoon.Sunday: A warm front is expected to sweep across the coast on Sunday. Expect light to moderate westerly winds combined with moderate precipitation. Freezing levels should gradually rise up to about 1200 metres.Monday: Light precipitation and moderate westerly winds combined with freezing levels rising during the day to about 1000 metres.

Avalanche Summary

We have a report from Thursday of a small size 1.0 skier/rider accidental triggered avalanche on a NE aspect at 1900 metres that released in the new snow. There have been no new avalanches reported releasing on the November rain crust.

Snowpack Summary

The recent very strong wind event has caused extensive wind scouring in the alpine and at treeline. Ski penetration is limited to about 15-20 cm above a stiff buried wind slab. Foot penetration may still be up to 70 cms as the wind slab is not able to carry the weight of a person without skis. The recent storm snow (up to about 130 cms) appears to be bridging above the early November weak layer, and we are not seeing deep releases down to the rain/ice crust. There is not much discussion about surface hoar that was buried last week, and we are not getting reports about test results on that layer. Professionals are concerned about the early November rain crust. If this deep persistent weak layer (DPWL) becomes reactive, the consequences will be very large destructive avalanches. The crust may be buried between 100-200 cms depending on the total depth of the snowpack in your area. The crust may be a bigger problem where it has a layer of facetted crystals above, rather than where it is like a laminated sandwich of crusts and facets. If that sounds too technical for you, then the take home is that this is not an easy problem to gauge when or where it might wake up.

Problems

Wind Slabs

Stiff wind slabs are now covered with an additional 10-15 cms of new snow. These wind slabs may be triggered from weak shallow areas like exposed rocks or trees on the edge of slopes.

Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.>Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 4

Deep Persistent Slabs

An old facet/crust combination deep in the snowpack may wake up with heavy triggers, smaller avalanches stepping down, or triggering from thin-spots, particularly on slopes with smooth ground cover.

Be aware of the potential for full depth avalanches due to deeply buried weak layers.>Be aware of thin areas that may propagate to deeper instabilites.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

3 - 7

Valid until: Dec 8th, 2012 2:00PM