Avalanche Forecast

Issued: Dec 19th, 2013 7:56AM

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

Peter, Avalanche Canada

Purcells.

Summary

Confidence

Fair

Weather Forecast

Friday: Cloudy with light to moderate snowfall around 5 cm. The freezing level is at valley bottom and ridgetop winds are light to moderate from the northwest. Saturday: Mainly cloudy with a chance of flurries and sunny breaks. The freezing level remains at valley bottom and moderate gusty northwest winds continue. Sunday: A mix of sun and cloud. The freezing level is near valley bottom and the upper flow continues to be northwesterly.

Avalanche Summary

One size 3 accidentally triggered slab avalanche was reported near Golden on Wednesday. This slide was triggered by a skier on a north-northeast aspect in the alpine and likely released on a persistent weakness near the bottom of the snowpack. The initial slide also sympathetically triggered another size 2.5 lower down the slope. Fortunately no one was buried or injured. Several other natural and explosive triggered avalanches (size 1.5-2.5) were reported - most were from the northern part of the region where up to 20 cm of new snow fell in the previous 24 hours. This type of avalanche activity may be a good indication of the potential for large avalanches during periods of loading.

Snowpack Summary

Up to 20 cm of low density new snow fell with the latest system, accompanied by moderate W-NW ridgetop winds. Expect to find dense wind slabs in exposed lee terrain at and above treeline. A couple notable persistent weak layers can be found in the top 60 cm. These layers have produced variable results with snowpack tests, but are increasingly concerning as the load above increases and/or a slab develops. If you're in the Golden area check out the latest update on local conditions from Skiing Golden. 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, north-facing slopes. Snow depth is still below threshold in many areas below treeline.

Problems

Wind Slabs

New snow and moderate to strong westerly winds have created dense wind slabs in exposed lee terrain and cross-loaded features. Rider triggering is possible, particularly in steep unsupported terrain.

Stay off recent wind loaded areas until the slope has had a chance to stabilize.>Avoid cross loaded slopes at or above treeline.>Use ridges or ribs to avoid pockets of wind loaded snow.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Deep Persistent Slabs

Triggering the persistent weakness of facets and/or a crust near the base of the snowpack is unlikely, but if it is triggered the resulting avalanche would likely be very large and destructive.

Avoid convexities or areas with a thin or variable snowpack.>Be aware of thin areas that may propogate to deeper instabilites.>Be aware of the potential for large, deep avalanches.>

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

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Dec 20th, 2013 2:00PM