Regions
Northwest Coastal.
Although conditions have improved, professionals and experienced riders are still making conservative terrain choices because of the potential for large persistent slab avalanches.
Confidence
High - Due to the number and quality of field observations
Weather Forecast
SUNDAY: Sunny with cloudy periods, light southeast winds, alpine temperatures around -5.MONDAY: Mix of sun and cloud, light west winds, alpine temperatures around -5.TUESDAY: Cloudy with scattered flurries along the coast, moderate southwest winds, freezing level rising to 500 m with alpine temperatures around -3.
Avalanche Summary
Evidence of widespread natural activity during last week's storm has been reported throughout the region. In the southern part of the region, size 2 to 3 avalanches released in the storm snow as well as on deeper surface hoar layers (likely the January 5th). Avalanches will become less likely at lower elevations as the wet snow freezes, however triggering storm and persistent slabs will remain possible at higher elevations.
Snowpack Summary
A warm wet storm delivered 40-60 cm of heavy snow in the south of the region, with freezing levels reaching 1200 m. Expect to find storm slabs at higher elevations, particularly on wind-loaded northeast slopes. At lower elevations, moist snow is freezing into a hard crust. At this point there is some uncertainty as to how deeper persistent weak layers are responding to the recent loading and warming. Several weak surface hoar and facet interfaces were reactive during the storm, but have shown signs gaining strength since. This includes the January 5th layer about 50 cm deep and the December 25th layer up to a metre deep. These are not typical conditions for this coastal region, and it will take more time to gain confidence about the distribution and likelihood of triggering these deeply buried weak layers.
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.