Avalanche Forecast

Issued: Dec 17th, 2013 8:24AM

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

bcorrigan, Avalanche Canada

Purcells.

Forecasters are operating with limited field data. If you've been in the back country recently, we'd love to hear from you. forecaster@avalanche.ca

Summary

Confidence

Fair - Due to the number and quality of field observations

Weather Forecast

Wednesday: Forecast models differ in precipitation amounts and intensity, but generally agree that Wednesday will have the most snowfall. 10 to 20 cmforecast for the Purcells.Thursday : Arctic air moves into the southern part of the province bringing freezing levels to valley bottom. No precipitation in the forecast.Friday: Cold arctic air will remain in the forecast region, with little or no precipitation expected

Avalanche Summary

Wind slabs overlying surface hoar and facets have become touchy. The possibility of triggering large and destructive avalanches is high. Recent reports speak of shooting cracks and widespread propagation in the storm and wind slabs. The potential exists for large destructive avalanches with increased loading and wind transport.

Snowpack Summary

Small amounts of recent storm snow are beginning to add up on top of the sugary facets from early December. Snowpack depths at tree line currently vary from 100- 130 cm, and reports speak of severe scouring on the windward side of ridges, resulting in snow deposition on lee slopes and creating dense wind slabs.A persistent weakness of buried surface hoar and facets is down approximately 20-40cm . This layer has been producing variable results with snowpack tests. Recent reports indicate that the new storm/wind slab is becoming reactive with warming temperatures and additional loads. At the base of the snowpack are weak facets and depth hoar, combined with a crust from early October.. 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 slopes. At lower elevations the snow depth is below the threshold for avalanches.

Problems

Wind Slabs

Conditions are tricky at tree line and above, with wind loaded features being the most complex. Several size 1 to 2 skier controlled avalanches have recently been reported around 2000 M.

Avoid cross loaded slopes at or above treeline.>Be aware of the potential for full depth avalanches due to deeply buried weak layers.>Carefully evaluate big terrain features by digging and testing on adjacent, safe slopes.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Wind Slabs

Be cautious as you transition into wind affected terrain.>Avoid freshly wind loaded features.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

Whumpfing is direct evidence of a buried instability.>Dig down to find and test weak layers before committing to a line.>Avoid convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Valid until: Dec 18th, 2013 2:00PM