Avalanche Forecast

Issued: Dec 6th, 2013 8:43AM

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

jfloyer, Avalanche Canada

Purcells.

Watch for pockets of wind slab on steep, convex terrain.

Summary

Confidence

Poor - Due to the number of field observations

Weather Forecast

Cold, clear weather looks set to continue through the weeekend.Saturday: Dry, temperatures around -28C, light NW winds.Sunday: Dry, temperatures around -22C, strong NW winds.Monday. A few flurries, maybe 1-2 cm new snow. Temperatures around -17C. Strong NW winds.

Avalanche Summary

No recent avalanche activity to report.

Snowpack Summary

Snowpack depth varies greatly across the region, averaging 70-110cm at treeline. The southern portion of the region received substantially more new snow (up to 70cm ) compared to the northern portion (as little as 10cm). The recent storm snow is sitting on top of the late-November interface which may consist of surface hoar on sheltered/shaded slopes, a melt-freeze crust on south facing slopes, or a combination of both in isolated locations. Strong NE winds after the storm have caused reverse loading and wind slab formation on SE through W aspects in wind exposed areas. In the southern part of the region there is 40-70cm of new snow over the late-November interface which has created a persistent slab problem. Expect the reactivity of this layer to increase when we eventually get warmer temperatures and new snow.In the northern part of the region the lower/mid snowpack is fundamentally weak, composed of an early season crust (more prevalent on north aspects) and weak faceted crystals. While many areas did not receive enough new snow to create a new slab problem on top of the late-November interface, there are likely isolated areas where a persistent slab does exist.

Problems

Wind Slabs

Recent strong northerly winds have redistributed fresh snow forming hard and soft wind slabs in exposed lee terrain. Windward slopes may be scoured and stripped of snow.

Avoid freshly wind loaded features.>Avoid traveling in areas that have been reverse or cross-loaded by winds.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Persistent Slabs

In deeper snow areas, it may be possible to trigger an avalanche on a layer of buried surface hoar. In shallower ones, watch for a sugary facet layer near the base of the snowpack.

Dig down to find and test weak layers before committing to a line.>Whumpfing, shooting cracks and recent avalanches are all strong indicators of unstable snowpack.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Valid until: Dec 7th, 2013 2:00PM