Several buried weak layers exist within the snowpack and have produced very large, destructive avalanches in recent days. Stick to moderate terrain and minimize your exposure to overhead hazard.
Weather Forecast
TONIGHT: Cloudy, light flurries. Accumulation trace. Ridge wind light, south. Temperature -12. Freezing level valley bottom.FRIDAY: Cloudy, light flurries. Accumulation 1-7 cm. Ridge wind light, south. Temperature -8. Freezing level valley bottom.SATURDAY: Cloudy, flurries. Accumulation up to 2 cm. Ridge wind light, southeast. Temperature -8. Freezing level valley bottom.SUNDAY: Cloudy, flurries. Accumulation 5-15 cm. Ridge wind light to moderate, south. Temperature -7. Freezing level valley bottom.
Avalanche Summary
Wednesday there was a report of a naturally-triggered Size 2.5 avalanche on a northwest aspect at 1900 m, with a crown 100 cm and is suspected to have failed on the early-January layer.On Monday, there was evidence of a widespread natural avalanche 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 and slid on a 30 to 35 degree north-facing slope.These types of avalanches are a continuing trend, showing that our snowpack is capable of producing very large, destructive avalanches even in relatively shallow terrain. Expect similar avalanches to release at all elevation bands where these buried weak layers are preserved.
Snowpack Summary
The current snowpack is complex, with three active weak layers that professionals are currently monitoring. Approximately 30-70 cm of storm snow sits on a layer of crust and/or surface hoar buried mid-January. The crust is reportedly widespread, with the possible exception of high elevation north aspects. The surface hoar is up to 10 mm is size and has been reported at all elevation bands. Deeper in the snowpack, the early-January persistent weak layer is found 40 to 90 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 with skier traffic. 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.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.