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Idaho Panhandle Avalanche Center

Avalanche Advisory

Good Morning, John "Oly" Olson with the Idaho Panhandle National Forest Avalanche Center. This advisory is valid for today, Christmas Eve, December 24th, 2010, plus an outlook for the Christmas and the 26th. This report does not apply to local ski areas within the forecast region and will remain in effect through midnight, December 24th. Thanks to Idaho Parks and Recreation for sponsoring this morning’s avalanche advisory. Thanks to John Pucci, Gene Klein and the Schweitzer Mountain Ski Patrol for their observations and Schweitzer’s support of weather instrumentation atop Schweitzer bowl.

WEATHER

It looks like the weather will be partly sunny today and through Christmas day with new snow starting Christmas night. Temperatures at elevation could go above freezing today and tomorrow. This could be enough to initiate point releases and propagate and entrain wet snow avalanches. National Weather Service in Spokane says that there could be between 4-8" of snow at elevation before Monday morning. The next several days could see continued snow with another 2-4" on Monday! What a great Christmas present! Avalanche hazard will increase in areas of heavy deposition and wind loading.

Avalanche conditions for the entire Idaho Panhandle National Forest Advisory Area are rated as Moderate on all aspects greater than 30 degrees above 5,000 feet. Natural avalanches are unlikely, human triggered avalanches are possible.

Avalanche conditions are rated as Considerable on wind loaded pockets above 6000’ above 35 degrees. Natural avalanches are possible and human triggered avalanches are probable.

Snowpack

Kevin and I were hosted by the Schweitzer Mountain Ski Patrol yesterday. They had avalanche results in the North Bowl that were impressive after the storm cycle last weekend. The major topic of discussion in the snow pack is the bomber crust that was laid down during the Dec. 13th rain event. This layer is supporting 8-14" of dry powder snow; true powder hounds are in search of. The southern Selkirk Mountains have received a series of small storms since the warm wet event with corresponding minor weak layers. The weak layer of concern is down at and below the crust with faceted snow and a temperature gradient. It appears to be going to equal temperature and bonding for the long term. In the short term and in the outlook period this layer could be triggered by heavy wind loading, melt freeze or travelers on very steep slopes.

Carole and Dan venture forth in the Lookout pass area yesterday. They found a buried surface hoar layer that was not very reactive about 4" down in a pack of nearly 4’ at the

FAA site at 5700’. Every one of these cold clear nights could lay down surface hoar depending on location. Spatial variability is one good reason to do your own snow studies to determine the avalanche hazard in your favorite area.

Terrain

Not a lot of snow out there yet so the shrubbery and logs and rocks are still poking out of the snow making it difficult to get around in all but the highest elevations. The crust layer has the pack well bridged down to about 4500’. At 5900’ in the Southern Selkirk Range on a north aspect we found nearly 6’ of snow. On a southern exposure at the same elevation there was about 50". There are lots of creek and hot holes from springs out there due to the wet season we’ve had in N. Idaho this year. Beware of creek crossings!