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: Flurries, accumulation 5-10cm / Moderate southwest wind / Alpine temperature -9 / Freezing level 1000m SUNDAY: Flurries, accumulation 5-10cm / Moderate to strong southwest wind / Alpine temperature -9 / Freezing level 900m MONDAY: Scattered flurries, accumulation 5cm / Light southwest wind / Alpine temperature -10 / Freezing level 800m
Avalanche Summary
Avalanche activity on Thursday included wind slabs, storm slabs and persistent slabs. Several wind slabs and storm slabs were reported to be running to size 2 on all aspects in the alpine and tree line. These were mostly natural triggers with one remotely triggered (from a distance) on a northeast aspect at tree line. A size 1 persistent slab avalanche 70cm deep was triggered by a skier at 1600m on a west aspect.On Wednesday persistent slab avalanches were human triggered to size 2 on north, northeast, southeast and west facing slopes between 1450 m and 2200 m. These ran on the early January and mid-December Persistent Weak Layers (PWL). Natural avalanches to size 2.5 were reported from steep alpine features that face northwest and southeast. Wind slab avalanches to size 1.5 were human triggered near ridge top. Bear in mind that this activity occurred before the most recent storm.
Snowpack Summary
The current snowpack is complex, we now have three active weak layers that we are monitoring. 20-40cm 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 5 to 20mm in size and was reportedly present up to 2100m and possibly higher. 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 80 to 150 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 200 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.