Avalanche Forecast

Issued: Dec 15th, 2013 8:34AM

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

bcorrigan, Avalanche Canada

Purcells.

Special attention to wind loaded terrain is necessary until the storm and wind slabs bond to the weak layers below.

Summary

Confidence

Fair - Due to the number and quality of field observations

Weather Forecast

Monday: Temperatures should lower slightly on Monday after the passing of the remnants of the Pacific frontal system on Sunday. Light precipitation, (2 to 5 cm), expected.Tuesday: Freezing levels will go up on Tuesday with light to very light precipitation expected, light to moderate sw winds at ridge tops.Wednesday: 2 to 5cm of precipitation with light winds from the west-south west, then temperatures going down as an arctic air mass in the north reaches down into the southern part of the Province.

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

Recent dribs and drabs of snow are adding to the snowpack surface load. Snowpack depths at tree line currently vary from 100- 130 cm with the highest variability in wind-exposed areas. 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 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

10 to 30 cm of wind and storm slabs now sit atop the surface hoar and facets from the early Dec. arctic cold snap. Reports indicate that these surface slabs are now becoming reactive. Shallow snowpack areas may be more easily triggered.

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 16th, 2013 2:00PM