Regions
Northwest Coastal.
New storm snow will be touchy on Saturday and lingering persistent weak layers are still a concern. Conservative terrain use is critical.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
FRIDAY NIGHT: Flurries with 10 cm of new snow and 30-50 km/h southeast winds.SATURDAY: Scattered flurries with 5-10 cm of new snow, 30-50 km/h southeast winds, alpine temperatures around -15.SUNDAY: Cloudy, moderate east winds, alpine temperatures around -12.MONDAY: Mix of sun and cloud, moderate to strong outflow (east) winds, alpine temperatures around -12.
Avalanche Summary
Another natural persistent slab avalanche was reported in the Ningunsaw area on Thursday, indicating that the persistent problem will linger for some time in the northern part of the region. No recent avalanches have been reported in the southern part of the region.On Saturday, the primary concern is fresh storm slabs with the new snow, although triggering deeper persistent layers remains possible.
Snowpack Summary
20-40 cm of new storm snow sits above a variable interface composed of hard wind slabs, weak surface hoar, and faceted snow. Expect the new snow to bond poorly to this interface and form extra touchy storm slabs on wind-loaded features. Below the new snow, a well settled slab sits above the Christmas surface hoar layer, which is now buried 40-80 cm deep and may still be reactive in sheltered areas. Deeper weak layers have only been reactive in areas with thin snowpacks. This includes a facet layer from early December that has been reactive in snowpack tests at lower elevations in the southern part of the region, and weak facets near the ground that have produced avalanches in the northern part 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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.