Areas of MODERATE avalanche danger will form today near and above treeline on the NW-N-NE-E-SE aspects on slopes 35 degrees and steeper as wind slabs continue to build. As higher intensity precipitation impacts the forecast area this evening through the overnight hours, avalanche danger is expected to increase to HIGH danger.
Strong winds today will scuplt new snow and wind transported old into wind slabs of increasing size. These new wind slabs will build on top of the small but unstable wind slabs that existed yesterday. Human triggered avalanches are possible today in near and above treeline terrain on NW-N-NE-E-SE aspects.
In areas above 9,500' persistent slabs linger near treeline and below treeline on NW-N-NE aspects. Weak layers of well developed facets and depth hoar remain buried in the snowpack in these areas and were not destroyed by rain on January 28 and 29. The likelihood of failure of these basal facets will increase as this storm cycle progresses and additional new snow load stresses the snowpack above these weak layers. Locations that are both above 9,500' and near treeline or below treeline terrain represent only a small portion of the forecast area, keeping this problem isolated in distribution.
Observations made yesterday on Carpenter Ridge (Independence Lake area) and near Grouse Rocks (Ward Canyon area) revealed small shallow wind slabs in lee areas and several weak layers within the upper snowpack on NW-N-NE aspects. Wind slabs were limited to 4 inches thick or less and generally extended less than 20 feet down slope. These wind slabs failed easily in response to the weight of a skier, producing shooting cracks and tiny avalanches. Upper snowpack weak layers consist of buried surface hoar, buried graupel layers, and/or near crust facets on top of the prominent January 30 rain crust. These weak layers have been observed in many locations around the forecast area over the past several days. The distribution of each of these weak layers varies around the forecast area, but generally 1 to 2 of these weak layers can be found in the upper snowpack on most NW-N-NE aspects. The presence of these weak layers has the existing snowpack in poor condition to handle new snow loading.
