Avalanche Forecast

Issued: Nov 27th, 2011 9:00AM

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

Avalanche Canada Peter, Avalanche Canada

Check out the Nov. 23rd post in the Forecaster's Blog for tips on how to manage risk immediately after a storm.

Summary

Confidence

Fair - Due to limited field observations

Weather Forecast

A ridge of high pressure should bring a mix of sun and cloud and light winds to the area on Monday. The freezing level should be around 600m. A weak system is forecast to bring increasing cloud and light snowfall on Tuesday (5-10cm) with a freezing level around 600-800m. On Wednesday expect a mix of sun and cloud and slightly warmer temperatures as another ridge becomes established.

Avalanche Summary

There have been few observers in the field during the storm but it is likely that a very widespread and large avalanche cycle occurred throughout the region on Saturday and into Sunday. One report mentioned hearing about large avalanches at all elevations, several of which ran full path to valley bottom runouts at 200-300m elevation. Natural avalanche activity should ease off early this week, but the potential for human triggered avalanches remains. Check out the Nov. 23rd post in the Forecaster's Blog for tips on how to manage risk immediately after a storm.

Snowpack Summary

Recent strong and shifting winds have created a variable snow surface and pockets of deep and dense wind slabs in exposed areas. Fluctuating freezing levels and heavy precipitation will likely produce various storm snow weaknesses. There is a persistent weakness of facets associated with a crust around 40-70cm above the ground. This weakness exists at treeline and alpine elevations and has been sensitive to human triggers. Several recent avalanches on this interface have shown very wide propagation and there have been cases of triggering from a distance. In some areas there is also a factet/crust layer just above the ground. This layer may still be a concern in areas with smooth underlying ground.

Problems

Wind Slabs

An icon showing Wind Slabs
Deep and dense wind slabs are likely well below ridge crests and in cross-loaded gullies and terrain features.

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

2 - 5

Persistent Slabs

An icon showing Persistent Slabs
Particularly touchy where there is an associated rain crust, which is prominent between 1800 and 2100m. Potential for remote triggering means that even low angle terrain may not be safe if there is exposure from above.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

2 - 5

Storm Slabs

An icon showing Storm Slabs

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 4

Valid until: Nov 28th, 2011 8:00AM

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