Avalanche Forecast

Issued: Dec 23rd, 2015 7:50AM

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

jlammers, Avalanche Canada

Purcells.

In some areas, wind slabs are still reactive to the weight of skiers and riders. Make observations continually as you travel.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Expect mainly a mix of sun and cloud for the forecast period, although clear skies may develop for Christmas day. Ridgetop winds should remain mainly light. Alpine temperatures should measure about -15 on Thursday, and then drop to about -20 on Friday and Saturday.

Avalanche Summary

Evidence of a few natural wind slab avalanches to size 2 was observed in lee alpine terrain on Monday and Tuesday. The avalanches occurred in response to new snow and wind on the weekend. On Wednesday morning in the Golden backcountry, a size 2 skier-triggered wind slab avalanche occurred on a northwest aspect at about 2400m. It was up to 50cm in depth and ran approximately 600m.

Snowpack Summary

Throughout last weekend there was up to 20cm of new snow. Strong southwesterly winds have redistributed much of this snow into wind slabs in exposed lee features in the alpine and at treeline. With the current cold weather, I'd suspect continued faceting in the snowpack. Areas most affected would include windward or cross-loaded rocky areas at higher elevations. Between 40 and 80cm below the surface you'll likely find a layer of weak buried surface hoar which is most prominent between 1400m and 1800m although it may extend to higher elevations in some parts of the region. Snow pit tests suggest that human triggering of this interface is becoming unlikely, although a release at this interface could be destructive in nature.

Problems

Wind Slabs

A size 2 skier-triggered wind slab avalanche was observed in the Golden area on Wednesday. This is a good reminder that recently formed wind slabs should remain on our radar and may still be sensitive to human triggering.

Stay off recent wind loaded areas until the slope has had a chance to stabilize.>Be cautious as you transition into wind affected terrain.>Avoid lee and cross-loaded terrain near ridge crests.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Persistent Slabs

A layer of buried surface hoar can be found between 1400m and 1800m. Although this layer has become less likely to trigger, I'd remain cautious on steep roles in cut-blocks and open glades below treeline.

Conditions are greatly improved, but be mindful that persistent weak layers are still present.>Avoid steep open slopes and convex rolls below treeline where buried surface hoar may be preserved.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Dec 24th, 2015 2:00PM