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 - Forecast snowfall amounts are uncertain
Weather Forecast
SATURDAY: Mix of sun, cloud and isolated flurries / Light to moderate southwest wind / Alpine temperature -10 / Freezing level 1100m SUNDAY: Flurries, accumulation 5-10cm / Moderate to strong south wind / Alpine temperature -10 / Freezing level 900m MONDAY: Scattered flurries / Light southwest wind / Alpine temperature -12 / Freezing level 800m
Avalanche Summary
On Thursday avalanche activity was reported as storm and persistent slabs. Storm slabs were running to size 2 on southerly and northerly aspects in the alpine and tree line. There were two persistent slab avalanches reported that were both skier triggered 80cm deep between 1100 and 1400m on north aspects. One of them was remotely triggered (from a distance) from 60m away and was a size 2.5. The other was triggered by a ski cut and was a size 1, yet still 80cm deep. On Wednesday a small natural avalanche cycle was reported from steep ridge features. Fast and loose sluffing was also reported.
Snowpack Summary
The current snowpack is complex, we now have three active weak layers that we are monitoring. 15-35cm 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 up to 10mm 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 30 to 60 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 100 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 100 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.