Avalanche Forecast

Issued: Dec 15th, 2011 8:49AM

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

Avalanche Canada swerner, Avalanche Canada

Summary

Confidence

Fair - Intensity of incoming weather is uncertain

Weather Forecast

Friday: Ridgetop winds will be blowing 70-90km/h from the north west. Snow amounts up to 10cm. Freezing levels will be at valley bottom. Treeline temperatures @1500m will be near -7. Saturday/Sunday: Mix of sun and cloud. Some flurries expected with minimal accumulations.

Avalanche Summary

Numerous rider triggered size 1 slab avalanches reported. These avalanches initiated from firm of pockets of wind slabs. They occurred on north-northwest aspects around 2100m.

Snowpack Summary

Up to 15cm of new snow fell earlier in the week. Beneath this new snow sits surface hoar up to 10mm in size. The surface hoar can only be found in sheltered areas. The strong wind that has been ripping through the region has kept the SH in check at upper elevations and exposed areas at treeline. This is a minor issue for the short term, but could be a significant player in the long term; this will be a layer to watch. It may not be reactive with 15cm, or will it? With drips and drabs in the forecast it makes it difficult to predict if, and/or when this layer may fail and initiate an avalanche cycle. The snowpack depth is still variable through the region. In upper elevations there are reports of up to a meter. The surfaces consist of firm wind slabs, surface hoar, and facetted (sugary) snow. Below the surface the mid pack seems to be holding strong. We are still concerned with the weak basal layers (rain crusts, facets) that exist at the bottom of the pack. The snowpack overall is still pretty thin. With numerous avalanches failing on this layer in the Rockies proves that there is still a chance for full depth avalanches to occur. When riding a slope try to avoid thin spots like small trees, shrubs or rock outcrops. These may react as trigger points, and initiate a deeper instability.There is a new Forecaster Blog Post today. It discusses "Dribs and Drabs" how incremental loading patterns will effect our snowpack. Please click the tab at page left.

Problems

Wind Slabs

An icon showing Wind Slabs
Expect new wind slabs on northeasterly aspects. Loading may occur lower on the slopes due to forecast high winds in some parts of the region.

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

An icon showing Persistent Slabs
With numerous avalanches failing on this layer in adjacent regions last week the potential for large, destructive full depth avalanches remains a concern.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 5

Valid until: Dec 16th, 2011 8:00AM