Regions
Northwest Coastal.
The storm slabs trend continues with more snowfall Tuesday adding to recent snowfall totals. As winds redistribute loose snow, expect deeper and more sensitive deposits in lee features and cross-loaded terrain.
Confidence
Moderate - Freezing levels are uncertain on Friday
Weather Forecast
TUESDAY NIGHT: Cloudy, with isolated flurries, trace accumulation. Light northwest wind. Alpine low -3C, freezing level 500 m.WEDNESDAY: Cloudy with isolated flurries, trace accumulation. Light to moderate west wind. Alpine high temperature -2C, freezing level below 1000 m.THURSDAY: Cloudy with scattered flurries, trace to 5 cm accumulation. Light south wind gusting strong. Alpine high +0C, freezing level rising above 1200 m.FRIDAY: Flurries and wet snow, 10-30 cm snow in the alpine. Moderate south wind gusting strong to extreme. Alpine high +2C, freezing level rising above 2000 m.
Avalanche Summary
Reports over the weekend have documented reactive slabs and evidence of recent avalanches. In the north of the region, storm slab, wind slab, and loose dry avalanches to size 2 were reported on Saturday and Sunday.Last 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.
Snowpack Summary
Up to 40 cm recent snow is being affected by wind forming slabs and loading snow in lee and cross loaded terrain. This snow covers a variable surface of wind-affected and faceted snow, a weak layer of surface hoar in more protected areas, and a rain crust/surface hoar combination below 1500 m. Forecasted rising freezing levels may result in moist snow below 900 m. Below the new snow interface, old wind-affected storm snow 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 last 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.
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.