Avalanche Forecast

Issued: Dec 7th, 2013 8:29AM

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.

swerner, Avalanche Canada

Purcells.

Summary

Confidence

Poor - Due to the number of field observations

Weather Forecast

The dominating arctic ridge continues, bringing cold and dry conditions through the forecast period.Sunday: Mainly sunny with cloudy periods. Alpine temperatures are showing a high of -20. Light ridgetop winds from the NW.Monday: Mix of sun and cloud. Alpine temperatures are showing a high of -15. Ridgetop winds strong from the West. Tuesday: A mix of sun and cloud. Alpine temperatures are showing a balmy -13. Ridgetop winds are light from the East.

Avalanche Summary

No recent avalanche activity to report.

Snowpack Summary

Snowpack depths at treeline vary across the region, averaging 70-110 cm. In the Southern part of the region there is 40-70cm of new snow over the late-November surface hoar/ crust/ facet interface that may be reactive, especially in sheltered northerly aspects where the surface hoar is better preserved.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 above and below the crust. This may be reactive from thin spot triggers, or larger triggers (sledder getting air time and dropping onto the suspect slope below). Strong NE winds after the storm have caused reverse loading and wind slab formation on SE through W aspects on open slopes and behind terrain features.While many areas did not receive enough new snow to create a new slab problem on top of these weak layers, there are likely areas where a persistent slab does exist.

Problems

Wind Slabs

Recently, strong winds from the North have redistributed storm snow, forming wind slabs in exposed lee terrain. Wind slabs found on these aspects are not typical, and they may surprise you.

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

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 weak sugary facet layer near the base of the snowpack.

Whumpfing, shooting cracks and recent avalanches are all strong indicators of unstable snowpack.>Dig down to find and test weak layers before committing to a line.>Conditions have slightly improved, but be mindful that deep instabilities still exist.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Valid until: Dec 8th, 2013 2:00PM