Avalanche Forecast

Issued: Dec 13th, 2012 9:23AM

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

slemieux, Avalanche Canada

South Columbia.

Watch for touchy windslabs at the top of the Treeline band.

Summary

Confidence

Fair

Weather Forecast

Very light accumulations are expected till tomorrow am with SW-NW moderate winds. The Western part of the region will see most of those precipitations. Sunny periods and broken clouds are still expected for Friday, seasonal temperatures throughout the whole period (-8 C) and light winds from the North West. The upper trough arriving on Saturday should bring light to moderate precipitations on the regions, again, with Westerly upslope seeing most of it. Winds should pick up to reach moderate to strong speeds from the South West. Another system is following for Sunday, its timing and intensity remain to see.

Avalanche Summary

A few small soft slabs were skier triggered on East and South aspects. An older (approximately from Dec. 10th) natural slab avalanche size 2.5 was also observed on an East facing windloaded convex slope. The crown was an average of 60 cm deep. There was also multiple releases from explosives that ran in the new snow from North West to South East facing slopes.

Snowpack Summary

Windslabs are still a concern in specific areas (Easterly aspects) in the alpine and at treeline with the forecasted light precipitations, moderate winds and the older snow available for transport. The new snow is also burying some older slightly deeper windslabs in sheltered areas. Overall, the upper snowpack is reported to be settling well. The November 28 surface hoar down 100-140 cm (between 1500 and 2000 m) is producing moderate to no results. The early November crust down 150-200 cm is also still a concern producing sudden collapses to no results. Professionals are still cautious in relation to these lingering deep problems, but the slow and improving trend hopefully allows us to step it down or even maybe take it out of the primary concerns in the near future.

Problems

Persistent Slabs

The weak layer is buried down about 100 cms and recently has been loaded by new snow and wind. Wind slabs above may trigger this deeper layer in unsupported terrain. Elevations between 1600-2100 metres are the most suspect.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 6

Deep Persistent Slabs

The early November rain crust is deeply buried. Releases on this layer will be very large and destructive.

Common trigger points for this kind of layer is thin rocky areas and areas with smooth ground cover.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

4 - 7

Wind Slabs

Be aware that windslabs may also be buried under the new snow in wind sheltered areas.

Use ridges or ribs to avoid pockets of wind loaded snow.>Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Valid until: Dec 14th, 2012 2:00PM