Potential for human triggering of large avalanches remains high. Now is the time to remain disciplined and stick to a conservative approach towards terrain.
Confidence
Moderate - Timing of incoming weather systems is uncertain on Sunday
Weather Forecast
FRIDAY: Mix of sun and cloud / Light southwesterly ridgetop winds / Alpine high of -11.SATURDAY: Cloudy with flurries; 5-10 cm of new snow / Moderate southerly ridgetop winds / Alpine high of -10.SUNDAY: 10-20cm of new snow / Moderate to strong southwesterly ridgetop winds / Freezing level rapidly rising to around 1500m.
Avalanche Summary
A size 3.5 natural deep persistent slab avalanche on a north aspect at 2600m was reported northwest of Edgewater on Wednesday. The layer was suspected to be the Mid-December layer and may have also stepped-down to the November crusts. Three additional size 2 natural deep persistent slab avalanches were reported on the same mid-December layer in the same area.
Snowpack Summary
The current snowpack is complex, with three active weak layers that we are monitoring.10-15 cm of new snow brings recent storm snow totals to 60-80 cm which overlies a crust and/or surface hoar layer (mid-January). The crust is reportedly widespread, except for possibly at high elevations on north aspects. The surface hoar is 10 to 30 mm in size and at all elevation bands. The recent snow fell with strong south winds, producing wind slabs and cornices in lee features. Deeper in the snowpack, a persistent weak layer known as the early-January layer is buried 50 to 80 cm, present at all elevation bands, and composed of surface hoar on sheltered slopes and sun crust on steep solar aspects. Recent snowpack tests have shown sudden fracture characters with moderate loads and high propagation potential, as well as other signs of instability such as whumpfs and cracking. Another persistent weak layer that was buried mid-December is 60 to 100 cm deep and consists of a facet/surface hoar/crust combination. 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.