Regions
Northwest Inland.
New snow and wind build will continue to build reactive slabs especially in wind-exposed areas. Choose conservative terrain and minimize overhead exposure. Large avalanches have been observed in the past week.
Confidence
Moderate - Intensity of incoming weather systems is uncertain on Wednesday
Weather Forecast
TUESDAY: Cloudy, flurries. Accumulation 5-10 cm. Ridge wind light to moderate, southwest. Temperature -3. Freezing level valley bottom.WEDNESDAY: Snow. Accumulation 10-15 cm. Ridge wind light gusting to strong, southwest. Temperature -1. Freezing level 1000 m.THURSDAY: Mix of sun and cloud. Ridge wind light, east. Temperature -7. Freezing level valley bottom.
Avalanche Summary
Reports have been limited. On Saturday a small storm slab was reportedly human triggered on an east facing aspect around 1000 m. At the start of the storm on Wednesday and Thursday skiers triggered a few small slabs on steep convex rolls.There are no recent reports of persistent slab avalanche activity, but some notable large avalanches occurred 5-8 days ago. This includes some large (size 2-3) natural persistent slab avalanches in the Howsons, and two large (size 2.5) remotely triggered avalanches north of Kispiox. We have no information from the Smithers area, but suspect a similar deeper weakness could exist there too. Activity on buried weak layers is most suspect during periods of heavy loading or rapid warming, hence it's time to be cautious.
Snowpack Summary
Approximately 30-50 cm of storm snow has accumulated since Thursday. The snow has mostly fallen as low density powder, but may have settled in some areas that experience a brief period of warming on Friday. A crust and/or weak feathery surface hoar layer buried in mid-January now lies 60-100 cm below the surface. The crust exists well into the alpine and the surface hoar can be found in sheltered areas in the lower alpine and treeline elevations. Another two crust / surface hoar layers that formed in December are buried 80-120 cm below the surface. These layers produced sudden results in recent snowpack tests and have been the suspected weak layer in recent large remotely (from a distance) triggered avalanches.
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.
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.