Avalanche Forecast

Issued: Dec 26th, 2013 8:45AM

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 - Track of incoming weather systems is uncertain on Friday

Weather Forecast

Friday: Light precipitation. Alpine temperatures -2. Moderate to strong southwesterly winds switching to northwest in the afternoon. Freezing level 1500mSaturday: Mainly dry with broken skies, winds moderate to strong from the northwest and alpine temperatures -7.Sunday: Light snowfall, alpine temperatures -9, winds light to moderate from the northwest.

Avalanche Summary

The deep persistent slab problem continues to be reactive up to size 3 with larger triggers such as explosives. Rider triggering is possible especially in shallow snowpack areas like rocky outcrops or near small trees.

Snowpack Summary

Up to 25 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

Moderate to strong west and southwest winds creating new windslabs in the lee of terrain features. A small wind slab release may be enough to trigger a deep weak layer, producing a large and destructive avalanche.

Be cautious as you transition into wind affected terrain.>Use ridges or ribs to avoid pockets of wind loaded snow.>Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Deep Persistent Slabs

The sensitivity to triggers is increased in shallow locations, especially on steep, convex, north-facing slopes.

Be aware of thin areas that may propogate to deeper instabilites.>Caution around convexities or areas with a thin or variable snowpack.>Use conservative route selection, stick to moderate angled terrain with low consequence.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 5

Valid until: Dec 27th, 2013 2:00PM