Regions
Northwest Coastal.
New snow fell in the south of the region, which will produce new storm slabs and load buried weak layers. Conservative decision-making is recommended, as large avalanches are likely.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
THURSDAY NIGHT: Cloudy with snowfall, accumulation 5 to 10 cm, moderate southwesterly winds, alpine temperature -6 C, freezing level 500 m.FRIDAY: Mostly cloudy, light northwesterly winds, alpine temperature -5 C, freezing level 800 m.SATURDAY: Mostly cloudy, light southwesterly winds, alpine temperature -6 C, freezing level 700 m.SUNDAY: Mostly cloudy, light southwesterly winds, alpine temperature -7 C, freezing level 400 m.
Avalanche Summary
On Wednesday, large (size 2.5) persistent slab avalanches were reported in the region at alpine and treeline elevations, being remotely triggered (from a distance), 50 to 150 cm deep, and on northeasterly aspects. Similarly, large (size 2) storm slabs were explosively controlled near Terrace on easterly to northeasterly aspects, with slab depths of 40 to 75 cm, at elevations around 1200 to 1350 m. Loose dry avalanches were also explosively controlled on easterly aspects.On Tuesday, numerous large (size 2-3) persistent slabs released remotely on a layer of surface hoar buried 40-60 cm deep in the Terrace area. This activity was focused on shaded aspects at treeline and below treeline elevations.
Snowpack Summary
Thursday's storm is expected to bring another 10 to 30 cm of snow to the southern parts of the region. This overlies last weekends 50 to 80 cm of storm snow, with the highest accumulation at high elevations and closest to the coast. Strong westerly winds have redistributed last weeks snow in open areas.Two layers of surface hoar exist in the region at depths of about 40 to 60 cm, being buried early and mid-March. At low elevations, a melt-freeze crust also exists.Numerous dormant layers exist deeper in the snowpack. Layers of crusts, facets, and isolated surface hoar buried 50 to 100 cm exist from mid- and late-February. A surface hoar/crust layer from January is buried around 150 to 200 cm. Near the bottom of the snowpack, weak and sugary facets exist in colder and dryer parts of the region, such as the far north.
Problems
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.
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.