Regions
Northwest Coastal.
Avoid avalanche terrain on Monday. A large natural avalanche cycle is expected.
Weather Forecast
SUNDAY NIGHT: Intense storm continues with another 20-30 cm of snow, extreme southwest winds, and freezing levels climbing.MONDAY: Another 10-20 cm during the day, extreme southwest winds, freezing levels peak at about 1000 m with alpine temperatures around -2 C .TUESDAY: The next pulse brings 10-30 cm starting late Monday night, strong southwest winds, freezing level dropping with alpine temperatures around -5 C.WENDESDAY: Lingering flurries with 10-20 cm, moderate southwest winds, alpine temperatures around - 7 C.
Avalanche Summary
No new avalanches were reported on Saturday. On Friday, a size 3 persistent slab avalanche was triggered on southwest slope by wind-loading on the February facets. There was also a report of a remotely skier-triggered avalanche on a small convexity, another sign persistent weak layers are primed for triggering.The current storm has all the ingredients for large widespread storm slabs. On top of that, it will also trigger very large persistent slab avalanches on buried weak layers.
Snowpack Summary
By Monday morning storm snow totals may reach 40-80 cm with deeper deposits in lee terrain. Rising temperatures will make the storms slabs very reactive. The new snow will also stress a weak interface from February composed of facets, crust, and surface hoar buried over a metre deep. This layer has produced avalanches and alarming snowpack test results on a regular basis for the past week. The lower snowpack is strong, with the exception of basal facets in shallow snowpack areas around Bear Pass and Ningunsaw.
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.