Avalanche Forecast

Issued: Dec 12th, 2011 9:32AM

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

Avalanche Canada ghelgeson, Avalanche Canada

Summary

Confidence

Fair - Due to variable snopack conditions

Weather Forecast

Yesterday's ridge of high pressure slides to the south as a weak system approaches from the west. No precipitation is expected and winds remain light out of the W, NW. Expect a daytime high of -6 with an overnight low of -13 under mostly sunny skies. A system tracks just south of the area Wednesday night into Thursday bringing scattered flurries to the region. The tracking is pretty sketchy at this point, but I think we'll get at least 2-5cm of snow, maybe a few more if the system moves a bit further north. Stay tuned for more details.

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. If you have any observations from the field, please drop us an email: forecaster@avalanche.ca.

Snowpack Summary

5 -10 cm of snow fell Sunday (111211) under light winds. Going forward, things are going to get interesting as this new snow fell on surface hoar (SH) crystals that average 10mm in size. This is almost the perfect recipe for a SH problem as most of the SH is likely well preserved under the new snow. This is a minor issue for the short term, but, this could be a significant player in the long term. If you're headed out into the field, I'd love to hear where you're seeing the surface hoar. I'd also be psyched to know if it's standing up or lying down. Thanks in advance for the observations.Upper elevation snow depths average a meter. Photos from the field show that the alpine is just barely open to travel in most places. The mountains look good from afar, but it's far from good above treeline where the snowpack is still pretty thin.It's been almost two weeks since our last significant storm and since that time the snowpack has suffered an unrelenting barrage of wind from around the compass rose leaving the snow wind damaged throughout most of the region. The saving grace for ski quality has been the cold temperatures which have faceted the upper 20 cm of the snowpack making for fun & fast skiing.The Rockies are home to a nasty raincrust /facet combo near the ground. This is the classic house of cards setup that professionals throughout the region are concerned about. With numerous recent avalanches failing in this layer in the Rockies recently the chance of a large full depth avalanche remains a concern. Triggering an avalanche in this weak layer will result in a large & destructive avalanche that will likely be unsurvivable.Stay conservative in your terrain selection and give the steep rocky slopes a miss, as these are the kinds of slopes where the weaknesses near the ground could still be triggered by the weight of a skier or sledder.

Problems

Wind Slabs

An icon showing Wind Slabs
New snow in combination with winds first from the East then shifting to the West have created soft slabs on all aspects at and above treeline.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Loose Dry

An icon showing Loose Dry
Watch for shallow loose snow avalanches in steep wind sheltered terrain. Know where your sluff is at all times to ensure that it doesn't push you where you don't want to go.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Likely - Very Likely

Expected Size

1 - 2

Persistent Slabs

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Valid until: Dec 13th, 2011 8:00AM