Regions
Northwest Coastal.
Conditions may vary significantly from South to North. Be sure to supplement this forecast with your own local observations.
Confidence
Fair - Forecast snowfall amounts are uncertain
Weather Forecast
Synopsis: Light snow, significantly cooler temperatures, and strong outflow winds are expected on Saturday as the Arctic front re-establishes near the coast. Another Pacific low and frontal system should make landfall on Sunday morning bringing moderate snowfall to the Northwest (10-20 cm). Valley outflows may continue but we should also see strong southerly ridge top winds. Light snow continues on Monday with freezing levels remaining at valley bottom.
Avalanche Summary
There were no reports of avalanches on Thursday, but conditions and visibility were likely poor and kept many observers out of the field. Watch for fresh, touchy wind and storm slabs to develop over the next couple days.
Snowpack Summary
Warm air invaded with the storm on New Years Day and brought rain or freezing rain up to at least treeline in southern sections, which may have squashed the surface hoar that was reportedly widespread before New Years. Temperatures cooled later in the day leaving 5-10 cm of new snow at lower elevations and around 20-25 cm at and above treeline. Further north (Bear Pass, Ninginsaw) it's more likely that the surface hoar layer is now buried by 15-20 cm of new snow. Strong W-NW winds have probably created fresh wind slabs in exposed lee terrain. Older hard slabs may also be lurking on South and West aspects from previous outflow winds. The mid December crust can be found down around 40 to 80 cm and is sandwiched with facets and surface hoar. The mid November crust down 70 to 175 is gaining strength but is still reactive in test profiles. It is likely trending towards dormancy.
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.