Regions
Northwest Inland.
Weak, sugary snow at the bottom of the snowpack remains a primary concern. This is especially true in large, steep, and rocky alpine features with variable snowpack depths.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
Tuesday: Clear skies / Moderate to strong northerly winds / Alpine temperatures of -15Wednesday: Clear skies / Moderate northerly winds / Alpine temperatures of -5Thursday: Light flurries / Extreme westerly winds / Alpine temperatures of -12
Avalanche Summary
A large natural slab avalanche was reported from the Babine Range on Sunday. The slab, which ran approximately 200m, was reported to be 50m wide and 50cm deep. The weak layer associated with this avalanche is unknown. Thanks to the individual who submitted the observation via the Mountain Information Network.
Snowpack Summary
10-20 cm of new snow fell last weekend. Observations have been limited, although I suspect these accumulations have likely been shifted into wind slabs at treeline and in alpine. Snow depth at treeline varies from about 1 m in most areas to 2 m in deeper snowpack areas in the south and west of the region, and up to 250 cm in the alpine. The shallow snowpack areas mostly consist of weak facetted or sugary grains beneath hard slabs. These hard slabs may produce surprisingly long fractures resulting in large avalanches, and in some instances they may step down to weak snow crystals near or at the ground. In addition to the facets, a thick layer of buried surface hoar may be found 30-40 cm below the surface. There is another persistent weakness that formed during the early December cold snap which is now about 50-70 cm deep. A crust from mid-November may be lurking close to the ground nestled in amongst the facets.
Problems
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
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.