Avalanche Forecast

Moderate - Forecast snowfall amounts are uncertain on Thursday

THURSDAY: Flurries increasing throughout the day with 5-15 cm of snow possible by the afternoon, moderate to strong southwest wind, freezing level rising to around 1400 m.FRIDAY: Another 5-15 cm of snow overnight and then clearing in the afternoon, light wind, freezing level dropping to around 800 m.SATURDAY: Mostly sunny, moderate south wind, freezing level rising to around 1500 m.

Persistent slab activity continued on Tuesday. A small wind slab on a northwest aspect in the McBride Range stepped down and triggered a much larger persistent slab avalanche when it reached 1900 m. The result was a size 3 avalanche (100 cm thick) that propagated across the entire bowl and ran all the way to the bottom of the valley. A few smaller size 1 natural slabs were also observed at and below treeline.Several persistent slab avalanches were reported last weekend, including a size 3 avalanche that was remotely triggered on a west aspect at 1900 m in the Blackcomb backcountry and presumably failed on a buried surface hoar layer (see photo and details here). At a similar elevation, a size 2 avalanche failed in a north-facing chute and triggered additional smaller avalanches on nearby slopes. Closer to Squamish, a natural size 2 avalanche failed on a south aspect at 1750 m (see photo and details here). These avalanches highlight a persistent slab problem that exists on all aspects around treeline elevations.

New snow will accumulate on Thursday and Friday and form extra deep deposits in wind loaded terrain. The new snow is falling on a sun crust on steep south-facing slopes, cold dry snow on polar aspects, and wind affected snow at upper elevations.Last week's storms buried a weak layer composed of soft facets, surface hoar, and/or crust that is roughly 50-100 cm below the surface. This layer has produced whumpfing, sudden reactive results in snowpack tests, and some remotely triggered avalanches. Lots of the activity has been on buried surface hoar on north aspects at upper treeline elevations. The snowpack is well settled and strong beneath this interface. Variable winds in the past month have produced cornices on many ridgelines. They will become touchier as they grow in size, as temperatures rise, and when they are subject to the strong late-winter sun on clear days.