Regions
Northwest Coastal.
Recently formed storm slabs and wind slabs will continue to be reactive to human-triggering. Conservative terrain selection remains very important.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain on Sunday
Weather Forecast
Unsettled conditions continue, bringing up to10 mm of precipitation Friday night. On Saturday, freezing levels will fall to 700 m with mostly cloudy skies and alpine temperatures of -3. Ridgetop winds will be light-gusting strong from the south. Sunday will see another pulse of precipitation 5-12 mm accompanied by moderate southwest winds. Alpine temperatures near -3 with freezing levels steady around 700 m. Monday will bring a mix of sun and cloud with alpine temperatures -5 and moderate winds from the south.
Avalanche Summary
On Thursday a skier triggered, deep persistent avalanche was triggered to size 2.5 from a SE aspect around 1700 m. There were also numerous explosive triggered storm slab avalanches up to size 2. These storm slabs will likely need more time to settle out and bond, so expect them to be touchy to rider triggers through the weekend. At lower elevations (1500m and below), widespread loose wet avalanches were stepping down to size 2 wet slabs. If the sun comes out, natural avalanches are possible on steep south facing terrain features. In the far north, deeply buried persistent weak layers may still be reactive to large triggers such as a small avalanche stepping down or a cornice failure.
Snowpack Summary
Recent storm snow accumulations are 40-80cm over the past week and overlie a melt freeze crust which extends up to around 2000m elevation. This recent snow is reported to be bonding well to the crust. Moist snow was reported below 1500m on Thursday and wet snow below 800m. Recent wind has redistributed the surface snow at higher elevations forming wind slabs in leeward features. The early January surface hoar/facet layer is down around 1m+ and remains a concern for commercial operations. This layer seems the most reactive in the north of the region but may still be a concern in the south as well. Shallow snowpack areas in the east and north of the region may have a weak base layer of facetted snow on or just above the ground.
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.
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.