Regions
Northwest Coastal.
Strong winds have probably redistributed snow and created wind slabs in a variety of places. Make conservative terrain choices and stay tuned to signs of instability.
Confidence
Fair - Due to the number of field observations
Weather Forecast
Synopsis: We should see a brief lull in the weather on Monday before the arrival of another strong frontal system late in the day. There could be a few breaks Monday morning followed by increasing cloud and snow in the evening. Overnight Monday and through Tuesday we could see 20-40 cm of snow. Winds increase once again to strong from the S-SW. The freezing level stays at valley bottom on Monday and Tuesday with treeline temperatures around -10. Snow and winds should gradually taper off on Wednesday. An above freezing layer might also form between 1000 and 2000 m.
Avalanche Summary
Several natural and explosive triggered wind slabs up to size 2 were reported on Saturday. Most of these were fresh wind slabs up to 40 cm deep from steep north-facing terrain near treeline. Wind slabs will probably remain sensitive to human triggers on Monday.
Snowpack Summary
Conditions are highly variable throughout the region. Southern sections near Terrace received around 30 cm of new snow while Bear Pass and Ninginsaw didn't see any new snow on Saturday night. Strong winds are one common theme in all areas though. Ridge winds have been cranking from the SE stripping windward slopes bare and probably forming hard or dense wind slabs in lee and cross-loaded areas. A buried surface hoar layer, down 25-35 cm, may be more prevalent in northern sections like Bear Pass and Ninginsaw Pass. The mid December crust can be found down around 40 to 80 cm and is sandwiched with facets and surface hoar. The November crust, down 70 to 175 cm, is gaining strength but is still reactive in some test profiles. The deeper snowpack weaknesses could 'wake up' with heavy loading from new snow and wind.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.
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.