Regions
Northwest Coastal.
Another heavy storm pulse will sustain very dangerous avalanche conditions on Tuesday.
Confidence
Moderate - Freezing levels are uncertain
Weather Forecast
TUESDAY: The next storm starts late Monday night bringing 20-40 cm, strong southwest winds, freezing level dropping with alpine temperatures around -3 C.WENDESDAY: Lingering flurries with 10-20 cm, moderate southwest winds, alpine temperatures around - 7 C.THURSDAY: Another 10-30 cm of snow, strong southwest winds, alpine temperatures around -7 C.
Avalanche Summary
A large natural avalanche cycle likely occurred during the peak of the storm on Sunday night. A few reports of small skier triggered slabs were reported in the early stages of the storm on Sunday, but poor visibility has limited field observations. Persistent slab avalanches on the February interface were reported on a daily basis prior to the storm. 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
Storm slabs will continue to grow on Tuesday with another 20-40 cm of snow and strong winds in the forecast. This comes in the wake of Sunday's 30-60 cm storm. The overall results will be widespread touchy storm slabs at higher elevations and unstable wet snow at lower elevations. The storm snow is also stressing a weak interface from February composed of facets, crust, and surface hoar buried over a metre deep. Given the recent activity on this layer before the storm, it should be very reactive during this storm. 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.