Regions
Northwest Coastal.
Up to 40 cm of snow fell in the south of the region. This snow formed storm slabs and is loading buried weak layers. Be cautious on southerly aspects when the sun is out. Conservative decision-making is recommended, as large avalanches are likely.
Confidence
Moderate - Timing or intensity of solar radiation is uncertain
Weather Forecast
SATURDAY: Sunny with afternoon clouds, light southwesterly winds, alpine temperature -6 C, freezing level 700 m.SUNDAY: Early-morning snowfall then partly cloudy, accumulation 5 to 10 cm, light northeasterly winds, alpine temperature -6 C, freezing level 700 m.MONDAY: Partly cloudy with afternoon snowfall, light southerly winds, alpine temperature -6, freezing level 600 m.
Avalanche Summary
On Thursday, large (size 2.5 to 3) storm and wind slabs were triggered naturally and by explosives, with slab depths up to 100 cm.On Tuesday and Wednesday, large (size 2 to 3) persistent slab avalanches and storm slab avalanches were reported in the region at alpine and treeline elevations, being remotely triggered (from a distance) as well as by explosives, 50 to 150 cm deep, and on northeasterly aspects.
Snowpack Summary
Thursday's storm dumped 30 to 40 cm of snow in the south of the region, such as around Terrace and Shames. This overlies last weekends storm snow, which was redistributed with strong westerly winds in exposed areas at higher elevations.Two layers of surface hoar exist in the region at depths of about 60 to 80 cm, being buried early and mid-March. At low elevations, the storm snow sits on a melt-freeze crust.Dormant weak layers exist deeper in the snowpack. Layers of crusts, facets, and isolated surface hoar from mid- and late-February are buried 100 to 150 cm. Near the bottom of the snowpack, weak and sugary facets exist in shallower 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.