Avalanche Forecast

Issued: Dec 8th, 2011 9:25AM

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

Avalanche Canada triley, Avalanche Canada

Check out the Forecasters Blog to see some of the things that we are discussing in the lead up to the weekend.

Summary

Confidence

Fair - Intensity of incoming weather is uncertain on Sunday

Weather Forecast

Continued high pressure across the interior mountain ranges on Friday and Saturday. The ridge should break down on Sunday when a weak low pressure moves across the interior. There may be some strong winds in the alpine when the light precipitation starts on Sunday.

Avalanche Summary

It is always important to know the history of the snowpack in the area that you want to explore. This season presents some challenges developing this baseline information due to the snow arriving well before most observers have started working in the field. It may be wise to take the time to dig down deep and see what the basement looks like in your regular play areas. There was one size 2.0 skier triggered slab avalanche in the South Selkirks that we know about from Monday. The slab was released by the third or fourth skier in a group, from a steep south aspect near the ridge top in the alpine. There are a few more reports from yesterday of old large avalanches that probably released around November 27th. A couple of large (size 2.0-2.5) natural avalanches have been reported releasing along the TCH highway corridor.

Snowpack Summary

The Surface Hoar continues to grow due to the clear and cold nights. Expect to find a sun-crust that has formed in the alpine on south through west aspects. I expect that the surface hoar will no longer be present on aspects that have developed the sun-crust. Wind slabs persist in the alpine and in large openings at treeline. The windslab has become less reactive to human triggers; however avalanches up to size 2.0 are still possible due to this problem. Some areas have a rain-crust below treeline from the 28th of November that has been buried by about 20 cms of snow. This rain-crust may be developing facets, and could become a layer of interest after it is buried by more of a load. There is still some concern associated with the early November buried surface hoar layer. This layer is buried down about 100-150 cms. Tests are showing that this layer is getting harder to release, and less likely to give clean and fast shears (Sudden Planar). If an avalanche does release on this layer, it is likely to be very large and destructive. Some areas also have a weak layer of facets at the base of the snowpack.

Problems

Wind Slabs

An icon showing Wind Slabs
Windslabs continue to be an issue in the alpine and in large openings at treeline. Reports suggest that triggering has become more stubborn.

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Persistent Slabs

An icon showing Persistent Slabs
Hard to trigger in most areas, but the consequences of triggering a slide on this layer may be a very large avalanche. Weaker thin spots around protruding rocks or clumps of small trees may be likely trigger locations.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 5

Valid until: Dec 9th, 2011 8:00AM

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