Avalanche Forecast

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

TUESDAY NIGHT: Cloudy with snowfall, accumulation 5-10 cm, moderate southerly winds, alpine temperature near -10 C, freezing level near valley bottom.WEDNESDAY: Mostly cloudy with intermittent snowfall, accumulation 2-5 cm, moderate to strong southerly winds, alpine temperature near -6 C, freezing level near 1100 m.THURSDAY: Cloudy with light snowfall, accumulation 5-10 cm, moderate to strong southerly winds, alpine temperature near -10 C, freezing level below valley bottom.FRIDAY: Partly cloudy, light southerly winds, alpine temperature near -10 C, freezing level below valley bottom.

On Monday, there was evidence of a widespread natural storm slab cycle with very large avalanches being released (up to size 3.5).  This occurred on all aspects, at all elevations, with depths of 40 to 100 cm, and generally occurring on the mid-January weak layer but sometimes on the mid-December layer.  Also, a large (size 2.5) persistent slab avalanche was triggered by a skier at treeline, which stepped down to the mid-December weak layer.  The slab was 65 cm deep, 30 to 35 degree incline, on a northerly aspect.  These types of avalanches are a continuing trend, showing that our snowpack is capable of producing very large, destructive avalanches even on relatively shallow terrain.  Expect similar avalanches to release at all elevation bands where these buried weak layers are preserved.

The current snowpack is complex, with three active weak layers that we are monitoring. 30-60 cm of storm snow sits on a crust and/or surface hoar layer (mid-January). The crust is reportedly widespread; high elevation north is likely one of the few crust-free zones. The mid-January surface hoar is up to 10 mm and reported at all elevation bands. The recent storm snow fell with strong south winds, producing wind slabs in lee features at treeline and alpine elevations and in open areas below treeline. Deeper in the snowpack, the early-January persistent weak layer is 30 to 70 cm below the surface. It is composed of surface hoar on sheltered slopes and sun crust on steep solar aspects and found at all elevation bands. Snowpack tests show sudden fracture characters with easy to moderate loads and high propagation potential, as well as whumpfs and cracking. Another weak layer buried mid-December consisting of a facet/surface hoar/crust combination is buried 40 to 100 cm deep. It is most problematic at and below tree line.A rain crust buried in November is 100 to 150 cm deep and is likely dormant for the time being.