Regions
Northwest Inland.
New snow and wind will load several buried weak layers in the snowpack. Choose conservative terrain and minimize exposure to overhead hazard. Large avalanches may run long distances.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
TONIGHT: Cloudy, flurries. Accumulation 5-10 cm. Ridge wind moderate, west. Temperature -4. Freezing level valley bottom.WEDNESDAY: Snow. Accumulation 10-15 cm. Ridge wind light to moderate, southwest. Temperature -6. Freezing level valley bottom.THURSDAY: Mostly cloudy, light flurries. Accumulation trace. Ridge wind light, northeast. Temperature -12. Freezing level valley bottom.FRIDAY: Sunny. Ridge wind light, northeast. Temperature -12. Freezing level valley bottom.
Avalanche Summary
On Monday evidence of a natural avalanche cycle from size 1.5-2.5 was reported on north through south aspects between 1200-1600 m in the Howson Range failing both in the recent storm snow as well as the deeper mid-December layer. A natural size 2.5 that failed on a deep weak layer of sugary, facets at the base of the snowpack was also reported from the northern part of the region near Ningunsaw.On Saturday a small storm slab was reportedly human triggered on an east facing aspect around 1000 m. And at the start of the storm on Wednesday and Thursday skiers triggered a few small slabs on steep convex rolls.Last week some large (size 2-3) natural persistent slab avalanches in the Howsons, and two large (size 2.5) remotely triggered avalanches north of Kispiox were reported. 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 last 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 were buried in December are now 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
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.