The snowpack is complex. Three active weak layers remain sensitive to human triggering. The easy solution is to choose simple terrain free of overhead hazard as the snowpack adjusts.
Confidence
Moderate - Timing of incoming weather systems is uncertain
Weather Forecast
SATURDAY: Mix of sun, cloud and isolated flurries / Light to moderate southwest wind / Alpine temperature -8 / Freezing level 1200m SUNDAY: Flurries, accumulation 5-10cm / Light to moderate southwest wind / Alpine temperature -8 / Freezing level 1200m MONDAY: Scattered flurries / Light to moderate southwest wind / Alpine temperature -10 / Freezing level 800m
Avalanche Summary
Avalanche activity on Thursday included wind slab, storm slab and persistent slab activity. Storm slabs were reported mostly to size 1.5 on all aspects at tree line. One size 3 naturally triggered persistent slab avalanche was reported in the south of the region running on a northeast aspect in the alpine. Natural and explosives triggered wind slab avalanches were reported running to size 2 on east and north aspects in the alpine and tree line.
Snowpack Summary
The current snowpack is complex, we now have three active weak layers that we are monitoring. 10-30cm of storm snow now sits on a newly formed crust and/or surface hoar interface. Prior to the storm the crust was reportedly widespread; high elevation north is likely one of the few crust-free zones. The now buried surface hoar is 10 to 30mm in size and was reportedly present at all elevations before the storm. Looking deeper, a persistent weak layer known as the early January interface is 40 to 80 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 at all elevation bands. Recent snowpack tests have shown sudden results with moderate loads. Additionally, yet another persistent weak layer buried mid-December consisting of a facet/surface hoar/crust combination, is buried 40 to 110 cm deep. It is most problematic at and below tree line. This interface is not thought to be present in the alpine.A rain crust buried in November is 90 to 150 cm deep and is thought to have gone 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.