Regions
Northwest Coastal.
Forecasts call for 20-30 cm snow with strong winds by Sunday morning. Expect the deepest and most reactive deposits in wind-loaded terrain. In areas accumulating over 35 cm new snow, avalanche danger is High.
Confidence
Low - Forecast snowfall amounts are uncertain
Weather Forecast
SATURDAY NIGHT: Periods of snow, 15-30 cm. Strong to extreme southwest winds. Alpine high temperatures around -6C.SUNDAY: Cloudy with flurries, 5-10 cm of new snow bringing new snow accumulation up to 40 cm. Moderate southwest winds gusting to extreme. Alpine high temperatures around -6C.MONDAY: Snow, 10-20 cm with accumulation starting later the day. Moderate south-southwest winds gusting strong. Alpine high temperatures around -6C.TUESDAY: Snow, 10-20 cm. Moderate southwest wind gusting strong. Alpine low temperatures around -4C.
Avalanche Summary
No avalanches were observed in most of the region over the last few days, but on Wednesday in the far north near Ningunsaw, two large (size 2 and size 3) remotely (from a distance) triggered persistent slabs were observed failing over a 20-50 cm-deep layer of surface hoar over crust. This problem is likely isolated to the far north of the region, but may also exist on sheltered high elevation slopes elsewhere in the region.Looking forward, steady light snowfall and high winds will be feeding a new wind slab problem into Sunday. Keep an eye on increasing new snow depths over the day and expect wind slab formation to occur more quickly at higher elevations.
Snowpack Summary
New snow is accumulating above surfaces that range from faceted (sugary) wind-affected snow in wind-exposed alpine areas to weak surface hoar over facets at protected higher elevations to surface hoar over rain crust below about 1500 metres. Below the new snow interface, the wind-affected storm snow from last weekend's storm is expected to have formed a good bond with the underlying snowpack. An exception to this 'good bond' may exist in some sheltered higher elevations that were unaffected by rain during the storm. Here, the old storm snow described above may overlie a weak layer of surface hoar (feathery crystals). This layer was identified as the failure plane in several recent large avalanches in the north of the region. It has not shown in reports elsewhere.For most of the region, a weak layer of facets (sugary snow) buried in early December exists down 180-250 cm. The likelihood of triggering this layer is decreasing, but it could be triggered by humans in shallow snowpack areas, particularly in the north of the region. The potential may also exist for large wind slab avalanches to step down to this layer, resulting in even larger 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.