Avalanche Forecast

Issued: Dec 6th, 2011 8:53AM

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

Avalanche Canada triley, Avalanche Canada

Summary

Confidence

Fair - Due to limited field observations

Weather Forecast

There may be a couple of cms of new snow overnight Tuesday into Wednesday morning. The ridge of high pressure should re-build early Wednesday bringing gradually clearing skies to the region. Thursday and Friday are forecast to be mostly clear and sunny with freezing down to the valley at night and rising slightly above the valley during the warmest part of the day. These conditions are prime for surface hoar to develop and continue to grow. We may continue to develop sun crust on steep slopes in the alpine that are exposed to the sunshine. Winds should be light from the west, but we may see some moderate outflow winds from the north in the alpine.

Avalanche Summary

We continue to hear reports of very large avalanches that released around the 27th of November. 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 have been no new avalanches reported in this region.

Snowpack Summary

Surface hoar has been forming over the last few 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 should be settling and becoming a bit more stubborn to trigger. Hard slabs in the alpine may propagate into large avalanches.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 4

Persistent Slabs

An icon showing Persistent Slabs
Probability of triggering has decreased. Where it still exists, this layer may be capable of producing highly destructive, full depth avalanches. Reactivity may also increase if temperatures rise.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Valid until: Dec 7th, 2011 8:00AM

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