Avalanche Forecast

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

TUESDAY: Partly cloudy, light to moderate northwesterly winds, alpine temperature near -10 C, freezing level below valley bottom.WEDNESDAY: Cloudy with snowfall, accumulation 2 to 5 cm, moderate westerly winds, alpine temperature near -5 C, freezing level near 1400 m.THURSDAY: Cloudy with snowfall, accumulation 5 to 15 cm, moderate westerly winds, alpine temperature near -10 C, freezing level near 1400 m and dropping to below valley bottom.

Numerous small to large avalanches were reported on Sunday, including storm slabs, wind slabs, persistent slabs, and deep persistent slabs. The largest avalanche was a size 4 natural avalanche on a northwest aspect at 2500 m, 200 cm deep, running for 1700 m, releasing on the late-November crust/facet layer described in the section below. The remainder of the reported avalanches were size 1 to 2.5 on all aspects, 1900 to 2600 m, 20 to 100 cm deep, which were triggered naturally, by skiers, and large loads. Cornices were observed to release naturally and by explosives, which triggered wind slabs below. Similar avalanches were reported on Saturday, showing a steady trend of avalanche activity.Looking forward, dangerous snowpack conditions will persist in the region 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.

Recent storms have produced variable new snow accumulations of 20-50 cm. Strong winds have produced wind slabs in lee features. This snow overlies a complex and generally weak snowpack structure with four active weak layers that we are monitoring:1) 70 to 110 cm of snow overlies a 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 10 to 30 mm in size and exists at all elevation bands.2) The early-January persistent weak layer is 80 to 130 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. Recent snowpack tests have shown sudden fracture characters with moderate loads and high propagation potential.3) Another weak layer buried mid-December consists of a facet/surface hoar/crust combination, which is buried 100 to 150 cm deep. It is most problematic at and below tree line.4) A crust/facet layer from late November is yet another weak layer, which has recently produced very large, destructive avalanches.