Avalanche Forecast

Issued: Dec 29th, 2013 8:27AM

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

Good

Weather Forecast

Monday: Light Flurries, alpine temperatures -5, freezing level at 1200m, winds moderate to strong from the west.Tuesday: Mainly cloudy with isolated flurries. Alpine temperatures -7 and freezing level at 1200m. Winds light to moderate from the west.Wednesday: Mainly dry with broken skies, alpine temperatures -8 with light winds from the west.

Avalanche Summary

Recent reports indicate a few naturally triggered avalanches to size 1.5 and 1 skier triggered avalanche running size 2. The skier triggered avalanche ran on a weak layer of facets 40cm below the snow surface on a southwesterly aspect in the alpine.

Snowpack Summary

Up to 25 cm of new snow from the past 5 days has been redistributed by moderate to strong northwest and southwest winds. These new windslabs cover older, stiff, dense wind slabs in exposed lee terrain at and above treeline. 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

Recent moderate and strong winds have created new windslabs that have buried old ones on a variety of aspects. A small wind slab release may be enough to trigger a deep weak layer, producing a large and destructive avalanche.

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Deep Persistent Slabs

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

Use conservative route selection, stick to moderate angled terrain with low consequence.>Caution around convexities or areas with a thin or variable snowpack.>Dig down to find and test weak layers before committing to a slope.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 5

Valid until: Dec 30th, 2013 2:00PM