Avalanche Forecast
Issued: Nov 29th, 2011 8:18AM
The alpine rating is Wind Slabs, Storm Slabs and Persistent Slabs.
, the treeline rating is , and the below treeline rating is Known problems includeSummary
Confidence
Fair - Due to limited field observations
Weather Forecast
Light-moderate snow amounts will end sometime Tuesday evening. A trough over the interior will move through to the east Wednesday morning bring a ridge of high pressure which will produce clear skys over the region into Thursday and Friday. Freezing levels could rise up to 1500m during the day, then lower back to valley bottom at night.
Avalanche Summary
In the Dogtooth range isolated natural avalanche activity wasobserved. These avalanches occurred from steep, rocky terrain at daysend Sunday, up to size 1.5 due to rapid loading. I suspect this mayhave been the norm through the region as the freezing level was at1800 meters and a surge of new snow and wind hammered through. Thismay be a good time to wait out the storm, let the new snow and thesnowpack settle, and make observations from your local s mountainswhen the visibility improves.
Snowpack Summary
Snow depths in the alpine are between 170 & 250cm. I suspect Sunday's warm, moist storm combined with strong southwesterly winds created stiff wind slabs on lee slopes, and some storm slab instabilities at upper elevations A highlighted concern for the Purcells was the mid-November storms that created a heavy slab over a weak basal faceted base. The Purcells saw a significant cycle of large avalanches running full depth as a result. (The Lizard Range also saw very similar results all failing on the weak basal layers.) . While the upper snowpack is likely tightening up, an avalanche triggered in the upper layers or initiated from a shallower spot in the snowpack could step down to weak basal facets at the ground creating large & unmanageable avalanches with very high consequences.
Problems
Wind Slabs
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Storm Slabs
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Nov 30th, 2011 8:00AM