Avalanche Forecast

Moderate - Timing, track, or intensity of incoming weather system is uncertain

TUESDAY NIGHT: Cloudy with snowfall, accumulation 10 to 20 cm, moderate westerly winds, alpine temperature near  -8 C, freezing level below valley bottom.WEDNESDAY: Cloudy with snowfall, accumulation 10 to 30 cm, moderate westerly winds, alpine temperature near -3 C, freezing level near 1500 m.THURSDAY: Cloudy with snowfall, accumulation 15 to 30 cm, moderate to strong westerly winds, alpine temperature near -6 C, freezing level near 1500 m.FRIDAY: Partly cloudy with possible valley cloud, light to moderate northwesterly winds, alpine temperature near -14 C, freezing level below valley bottom.

Many slab avalanches were reported in the region on Monday, including storm/wind slabs and persistent slabs.  The storm and wind slabs were generally 20 to 50 cm deep, but as deep as over 100 cm, likely in wind-loaded features.  They were on all aspects, all elevations, and triggered naturally, by explosives, and skiers.  The persistent slab avalanches released on all of the layers discussed in the section below, they were between 100 and 400 cm deep, on northerly and easterly aspects, and triggered naturally and by explosives.  Similar avalanches were reported between Friday and Sunday, showing a steady trend of avalanche activity.Looking forward, dangerous snowpack conditions will persist in the region, particularly with forecasted snowfall on Wednesday.  This trend will likely continue until a more stable weather pattern governs and we see a decrease in avalanche observations. All of our buried weak layers (described below) continue to produce large, destructive avalanches from natural and human triggers. Recent storm slabs and wind slabs have the potential to step down to deeper weak layers, which could produce large, destructive avalanches.

Up to 50 cm of snow could accumulate on Wednesday. This overlies 100-200 cm of storm snow from the past two weeks that has formed widespread storm slabs and wind slabs in lee features, which sit over an unstable snowpack. There are four active weak layers that we are monitoring:1) 80 to 150 cm of storm snow sits on the crust and/or surface hoar layer from mid-January. The crust is reportedly widespread, except for possibly high elevation north aspects. The surface hoar is 5 to 20 mm in size and was reported up to tree line elevations and possibly higher. This layer is the primary weak layer of concern and remains within the depth range of human triggering.2) The early-January persistent weak layer is 120 to 170 cm below the surface. It is composed of surface hoar on sheltered slopes as well as sun crust on steep solar aspects and is found at all elevation bands.3) Another weak layer buried mid-December consists of a facet/surface hoar/crust combination, which is buried 150 to 200 cm below the surface. It is most problematic at and below tree line.4) A crust/facet layer from late November is yet another failure plane responsible for recent very large avalanches.