We have a complex snowpack: touchy storm and wind slabs sit above three weak layers that are reactive to natural and human triggers at all elevations. Perform cautious route-finding without overhead exposure as the snowpack adjusts to the load.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
TUESDAY: Mostly cloudy with intermittent snowfall, accumulation 3-7 cm, moderate to strong southerly winds, alpine temperature near -10 C, freezing level near 500 m.WEDNESDAY: Mostly cloudy with intermittent snowfall, accumulation 10-15 cm, light to moderate southerly winds, alpine temperature -7 C, freezing level near 700 m.THURSDAY: Mostly cloudy with light snowfall, accumulation 5-10 cm, moderate to strong southerly winds, alpine temperature near -10 C, freezing level near 500 m.
Avalanche Summary
On Sunday, numerous small to large (size 1 to 2) storm slabs and loose dry avalanches were triggered naturally and by skiers, generally failing on the mid-January weak layer. Three persistent slabs between size 1 and 3.5 were observed, being triggered naturally and by skiers in treeline and alpine terrain on all aspects. These sorts of avalanches have been a consistent trend since last Wednesday, with small to large storm slabs observed at all elevations and large persistent slabs most often observed at treeline and alpine elevation bands. Being triggered naturally and by skiers and snowmobilers. These avalanches have been releasing on all three persistent weak layers described in the Snowpack Discussion. Expect similar avalanches to release, as our snowpack adjusts to the recent load.
Snowpack Summary
The current snowpack is complex, with three active weak layers that we are monitoring.50-80 cm of storm snow sits on a crust and/or surface hoar layer (mid-January). The crust is reportedly widespread, except for possibly at high elevations on north aspects. The mid-January surface hoar is 5 to 20 mm in size and was reported at treeline elevations and possibly higher. The recent storm snow fell with strong south winds, producing wind slabs in lee features at treeline and alpine elevations and in open areas below treeline. Deeper in the snowpack, the early-January persistent weak layer is 80 to 100 cm below the surface. It is composed of surface hoar on sheltered slopes as well as sun crust on steep solar aspects and is found at all elevation bands. Snowpack tests show sudden fracture characters with moderate loads and high propagation potential, and signs of instability such as whumpfs and cracking. Another weak layer buried mid-December consisting of a facet/surface hoar/crust combination is buried 100 to 150 cm deep. It is most problematic at and below tree line.A rain crust buried in November is generally 150 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.