Avalanche Forecast

Issued: Dec 16th, 2013 8:18AM

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.

Timing and intensity of the next snowfall is uncertain. Hazard may go up with increasing load from incoming storms.

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain

Weather Forecast

Tuesday: Freezing levels will go up on Tuesday with light to very light precipitation expected, light to moderate sw winds at ridge tops.Wednesday: Forecast models differ in precipitation amounts and intensity, but generally agree that Wednesday will have the most snowfall. 10 to 20 cm forecast for the Purcells.Thursday : Arctic air moves into the southern part of the province bringing freezing levels to valley bottom.

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, moving snow onto lee sides 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. With increasing load the weak layers may become more reactive.

Problems

Wind Slabs

Wind and storm slabs overlie the sugary faceted snow that formed in early December. Several size 1 skier controlled slab avalanches have been reported in the last few days.

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

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Wind Slabs

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

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Valid until: Dec 17th, 2013 2:00PM