Avalanche Forecast

Issued: Dec 25th, 2013 8:34AM

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

mbender, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather system is uncertain on Thursday

Weather Forecast

Thursday: Cloudy with some sunny breaks. Alpine temperatures -2. Ridgetop winds light-moderate from the South. Freezing levels rising to 1600 m.Friday: Snow amounts up to 8 cm. Alpine temperatures near -4. Freezing levels 1000 m.Saturday: Mainly cloudy with isolated flurries, alpine temperatures -9, light westerly winds.

Avalanche Summary

The deep persistent slab problem continues to be reactive up to size 2 with larger triggers such as explosives. Rider triggering is possible especially in shallow snowpack areas like rocky outcrops or near small trees. Additionally on Monday a natural size 2 avalanche was reportedly seen from a NE aspect at 2300 m.

Snowpack Summary

Up to 20 cm of new storm snow covers stiff, dense wind slabs in exposed lee terrain at and above treeline. Average snowpack depths at treeline elevations are 100-130 cm. In the upper 80 cm of the snowpack a couple persistent weak layers exist, comprising of surface hoar and a facet/crust combo. This interface has produced variable results with snowpack tests, and operators are keeping a close eye on them as the load above increases and/or a slab develops.A bigger concern, especially in the Northern part of the region where the snowpack is thinner and more variable is weak faceted and depth hoar crystals combined with a crust from early October. This is now down around 80-120 cm. This deep persistent weakness may be stubborn to trigger, especially in deeper snowpack areas, but the sensitivity to triggers likely increases in shallower locations, especially on steep, convex, north-facing slopes.

Problems

Wind Slabs

New snow and wind has formed wind slabs over the old dense wind slabs. A small wind slab release may be enough to trigger a deep weak layer, producing a large and destructive avalanche.

Stick to well supported, lower angle terrain.>Avoid lee and cross-loaded terrain near ridge crests.>Avoid steep lee and cross-loaded features>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Deep Persistent Slabs

The sensitivity to triggers will likely increase in shallow locations, especially on steep, convex, north-facing slopes.

Be aware of thin areas that may propogate to deeper instabilites.>Avoid convexities or areas with a variable snowpack.>Be aware of the potential for large, deep avalanches.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 5

Valid until: Dec 26th, 2013 2:00PM