Avalanche Forecast

Issued: Dec 25th, 2014 8:14AM

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

swerner, Avalanche Canada

Purcells.

Conservative decision making and terrain use is the name of the game when these tricky avalanche conditions persist. Check out the new Forecaster Blog @ avalanche.ca.

Summary

Confidence

Fair - Due to the number of field observations

Weather Forecast

A ridge of high pressure is strengthening a predominant northwesterly flow which will invade the Interior regions. This will bring relatively dry cool air. Ridgetop winds will blow light-moderate from the northwest and alpine temperatures will hover near -15. Skies will likely remain cloudy with some sunny periods Friday and Sunday. Light precipitation is expected Saturday.

Avalanche Summary

On Thursday, explosive controlled size 2.5 occurred and stepped down to the deep persistent early November rain crust. The mid-December buried surface hoar layer remains touchy to skier and rider triggers with several avalanches up to size 1.5 on Wednesday. I don't expect things to improve over the holiday period and suspect this layer is primed for human triggers. Remote triggering up to 100 m is still a concern.

Snowpack Summary

New snow 10-20 cm fell Tuesday night, with southern locations seeing the higher amounts. This brings storm snow totals 30-70 cm above a very touchy surface hoar layer that was buried mid-December. Below 2100 m this slab sits on a thick, solid crust that has been acting as a perfect sliding layer. This persistent slab remains touchy to the weight of a skier and rider, especially in wind effected areas. A hard rain crust with facets from early November is buried over 1 m down and is currently unreactive, however; triggering from shallow rocky and unsupported terrain remains a concern and should be kept on your radar.

Problems

Persistent Slabs

A very touchy surface hoar layer is buried by a 30-70 cm thick persistent slab. This layer is widespread, and is easily triggered by skiers and riders. Remote triggering with wide propagation is a concern.

Use conservative route selection, dig down and test weak layers before committing to anything. >Stick to simple terrain, small features with limited consequence and be aware of what is above you at all times.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Deep Persistent Slabs

A hard rain crust buried 1-1.5 m down seems to be unreactive, however; likely trigger spots are thin rocky and unsupported terrain, or from shallow snowpack areas.

Conditions may be worse in the north of the region, so get to know your local snowpack.>Be aware of thin areas that may propogate to deeper instabilites.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Valid until: Dec 26th, 2014 2:00PM