Avalanche Forecast

Issued: Dec 24th, 2013 8:13AM

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.

swerner, Avalanche Canada

Purcells.

The snowpack structure is complex and varies throughout the region. A conservative approach is essential.

Summary

Confidence

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

Weather Forecast

It looks like the Interior Mountains will see snow for Christmas, as a stream of moisture spreads from North – South Wednesday afternoon and overnight into Thursday. I'm uncertain with timing, however most model runs are agreeing with precipitation amounts.Christmas Day: Snow amounts 5-10 cm. Alpine temperatures -6. Ridgetop winds moderate from the SW.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 tapering up to 8 cm. Alpine temperatures near -4. Freezing levels 1000 m. Special Notice: Our radar has just picked-up what appears to be a flying sleigh. Our forecasters believe the sleigh belongs to Santa as it is being pulled by at least 8 reindeer. The sleigh is now in the far north of the province at the 2000m elevation and is currently headed south. More information will be posted as it becomes available.

Avalanche Summary

The deep persistent slab problem continues to be reactive with larger triggers like explosives up to size 2. I suspect this can also still be triggered under the weight of a skier or rider, especially from thinner snowpack areas, or thin spot trigger points like rocky outcrops. 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. Rider triggering is likely and a small wind slab release may be enough to trigger a deep weak layer, producing a large-very large avalanche.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Deep Persistent Slabs

May be stubborn to trigger, especially in deeper snowpack areas. The sensitivity to triggers will likely increase in shallow locations, especially on steep, convex, north-facing slopes. If triggered, consequences can be devastating.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 5

Valid until: Dec 25th, 2013 2:00PM