Regions
Northwest Coastal.
Storm snow and strong winds have formed deep and touchy slabs particularly at treeline in the Shames area. Choose conservative terrain and be aware of overhead hazards. Recent very large avalanches have run long distances.
Confidence
Moderate - Wind effect is extremely variable
Weather Forecast
TONIGHT: Light flurries. Accumulation trace. Ridge wind strong, east. Temperature near -5. Freezing level valley bottom.FRIDAY: Mix of sun and cloud. Ridge wind moderate, northeast. Temperature near -5. Freezing level valley bottom.SATURDAY: Sunny. Ridge wind light, east. Temperature near -8. Freezing level valley bottom.SUNDAY: Sunny. Ridge wind light, west. Temperature near -5. Freezing level valley bottom. Alpine inversion.
Avalanche Summary
Explosive control work on Thursday produced very large destructive storm slab results from size 3-4+ on north and south aspects the Skeena corridor, as well as a remotely triggered (from 400 m away) size 2, storm slab at treeline in the Shames area. On Wednesday and Tuesday we received a reports of a large (size 3-3.5) natural cycle as well as two very large (size 4 and 4.5) natural avalanches that failed in deeply wind-loaded areas. The larger of these occurred near Snowbound Creek west of Terrace on a south aspect at 1400 m and ran full path from ridge top to valley bottom, destroying a significant amount of mature forest beyond it's historical trimlines. There was also a report of a size 2 skier-triggered cornice release on Wednesday that occurred on a northeast aspect at 1300 m, northwest of Terrace.On Tuesday skier controlled and natural wind slab avalanches up to size 2 were also reported on north to east aspects between 1200-1400 m.Evidence of a widespread natural cycle up to size 3 was reported Monday while explosive control work on Monday produced numerous size 2.5 - 3 storm slabs on southeast through southwest aspects at all elevations.
Snowpack Summary
Recent storm snow accumulations of 50-100 cm have buried old, hard wind slabs and scoured surfaces in wind-exposed areas. In wind-sheltered terrain, sun crusts or dry facets sit below the recent storm snow.In the upper pack about 100-150 cm deep, is an interface of sun crusts, facets and spotty surface hoar (which is most prevalent in sheltered treed locations) that was buried mid-February. Deeper in the snowpack, around 150-200 cm down, you'll find a crust/surface hoar layer from January which still has the potential to be triggered from a thin snowpack spot, or with a large trigger like cornice fall. Basal facets may be found near the bottom of the snowpack in colder / drier parts of the region.
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.