The snowpack is complex and being loaded by new snow and strong winds. Three weak layers are reactive to natural and human triggers. The easy solution is to choose simple terrain free of overhead hazard as the snowpack adjusts.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
MONDAY: Cloudy with intermittent snowfall, accumulation 5-10 cm, light to moderate southwesterly winds, alpine temperature near -9 C, freezing level near 900 m.TUESDAY: Mostly cloudy with intermittent snowfall, accumulation 2-5 cm, light to moderate southerly winds, alpine temperature near -9 C, freezing level near 700 m.WEDNESDAY: Mostly cloudy with intermittent snowfall, accumulation 5-10 cm, light to moderate southerly winds, alpine temperature -5 C, freezing level near 1000 m.
Avalanche Summary
On Saturday, small to large (size 1 to 2.5) wind slabs and storm slabs were noted on all aspects at treeline and in the alpine, generally releasing on the mid-January weak layer. Numerous small to large persistent slab avalanches on the early-January weak layer were also observed from skiers and explosives in the southwest of the region.On Friday, there were several reports of small to large (size 1 to 3) storm slab, wind slab, and persistent slab avalanches, triggered naturally and by skiers. Similar avalanches were reported on Wednesday and Thursday. These avalanches have been releasing on all three persistent weak layers described in the Snowpack Discussion.
Snowpack Summary
The current snowpack is complex, we now have three active weak layers that we are monitoring.40-60 cm of storm snow now sits on a newly formed crust and/or surface hoar layer (mid-January). Prior to the storm, the crust was reportedly widespread, except for possibly at high elevations on north aspects. The buried mid-January surface hoar is 5 to 20 mm in size and was reportedly present at all elevations before the storm. Deeper in the snowpack, a persistent weak layer known as the early-January layer is 50 to 90 cm below the surface. It is composed of surface hoar on sheltered slopes as well as sun crust on steep solar aspects and is present to at least 2100 m, possibly higher. 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. Yet another persistent weak layer buried mid-December consisting of a facet/surface hoar/crust combination, is buried 90 to 150 cm deep. It is most problematic at and below tree line. This layer is not thought to be present in the alpine.A rain crust buried in November is 100 to 200 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.