Avalanche Forecast

Issued: Dec 13th, 2011 9:05AM

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 - Due to variable snopack conditions

Weather Forecast

Wednesday: Mainly dry cold conditions during the day. 3-5cm expected to fall Wednesday night with moderate south west winds. Treeline temperatures near -10. Thursday: Expected flurries up to 5cm ending in the afternoon with manly dry cold conditions through to Saturday. Freezing levels will remain at valley bottom.

Avalanche Summary

There were numerous avalanches both natural and human triggered from Size 2 - 3 in the adjacent forecast areas last week where avalanches failed near the ground on the crust/facet combo.

Snowpack Summary

Up to 15cm of new snow fell Sunday through Monday.Under this new snow sits surface hoar up to 10mm in size. I think the surface hoar can only be found in sheltered areas. The strong wind that has been ripping through the region has probably kept the SH in check at upper elevations, or exposed areas at treeline. This is a minor issue for the short term, but, this 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 create an avalanche cycle. The snowpack depth is still variable through the region. In upper elevations there are reports of up to a meter. The top part consisting of firm wind slabs, surface hoar, and facetted (sugary) snow. Below that 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.

Problems

Wind Slabs

An icon showing Wind Slabs
Recent strong westerly winds have created new wind slabs on lee slopes. Watch for pockets of wind slab in unsuspecting places behind features or lower on the slope.

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Possible - 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

3 - 6

Valid until: Dec 14th, 2011 8:00AM