Incremental storm snow may be settling into a cohesive slab above buried weak layers, allowing for longer fractures and resulting in larger avalanches. Wind loaded pockets may be deep and easily triggered.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain on Thursday
Weather Forecast
Another 5-10 cm of new snow combined with moderate southwest winds overnight as the freezing levels drop back to valley bottoms. Flurries or periods of light snow on Thursday combined with moderate northwest winds and alpine temperatures around -5. Some flurries expected on Friday with a chance of broken skies in the afternoon; winds light southwest and alpine temperatures around -10. Increasing southwest winds on Saturday with increased cloud and some flurries or light snow.
Avalanche Summary
Storm slab avalanche up to size 3.0 in the Rogers Pass today. Other operations have reported mostly size 1.5 natural avalanches. One report from the southern Monashees of skier remotely triggering a storm slab about 50 cm deep above surface hoar in a cut block at 1600 metres elevation. Numerous avalanches were reported on Tuesday up to size 2.0 but mostly size 1.0-1.5 that were releasing as storm slabs or loose dry avalanches. Expect storm slabs to continue to be easy to trigger on Thursday. Pockets of wind transported snow may be deep and propagate where they are sitting on weak buried crystals and/or old melt-freeze crusts.
Snowpack Summary
Another 10-15 cm of new snow has combined with recent snow to make storm snow totals of 20-40 cm. Some areas have reported a thin freezing drizzle crust on the surface before the Wednesday morning snow arrived. Storm slabs now overlie a variety of touchy weak layers. Storm and wind slabs will likely continue to build with forecast snow overnight. There is about 50 cm above the surface hoar, facets, and sun crusts that were buried early in January. The mid and lower snowpack are generally well settled and strong.
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.