New snow continues to add to the developing storm slab. The next Pacific storm should arrive on Thursday.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
A chance of light flurries overnight and during the day on Wednesday combined with moderate Southwest winds and temperatures around -10 in the alpine. The next storm should hit the coast early Thursday morning and then quickly move inland where it is expected to collide with the arctic air descending from the North. Expect 5-10 mm of precipitation that may be 10-20 cm of snow combined with strong Southwest winds and alpine temperatures which may be warmer than the valleys as the warm Pacific air moves over the cold arctic air. Expect another 8-12 mm of precipitation that may be 15-25 cm of snow by Friday morning and another 10-20 cm during the day. The storm should continue through Saturday.
Avalanche Summary
There were numerous small size 1.0 Loose dry and soft storm slab avalanches releasing at the storm snow/crust interface, or pockets of wind transported snow at ridgetops.
Snowpack Summary
The new storm slab is 30-50 cm and sits on a variety of old surfaces. A crust can be found below about 1900m in the north of the region and below 2200m in the south of the region. At higher elevations the new snow covers old wind slabs formed by moderate southwest winds. Several persistent week layers can be found deeper in the snowpack that may be capped by the overlying crust at lower elevations. The mid-January surface hoar is buried between 40 and 80cm down and remains a concern at treeline and above. The mid-December surface hoar layer is now 80 to 140cm below the surface and appears to be slowly gaining strength.
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.