Regions
Kootenay Boundary.
Avalanche danger will rise over the forecast period due loading from new snow, wind, or rain.
Weather Forecast
Freezing levels are expected to climb out of valley bottoms with the onset of snowfall on Thursday and rise above 2000 m by Friday afternoon. Precipitation is expected to arrive in three separate waves of increasing intensity over the forecast period. Expect 10-20 mm falling mostly as snow (around 15 cm) by Friday morning, then another 10-20 mm turning to rain below 2000 m throughout the day on Friday, with another 15-30 mm on Saturday. Ridge top winds are expected to peak on Friday afternoon with strong southwesterlies.
Avalanche Summary
New avalanche activity includes skier and explosive controlled wind slab avalanches up to Size 2, as well as an accidentally triggered 30cm thick persistent slab avalanche that ran on the mid-December buried surface hoar.
Snowpack Summary
Light amounts of new snow adds to the 5-20 cm sitting on a widespread hard crust that is topped by large surface hoar. This combo has been reported on all aspects and elevations, but so far weak slabs have been limited to wind-loaded slopes. The mid-January weak layer of buried surface hoar is down 25-65 cm and continues to give planar results in snow profile tests. The mid-December crust/facet/surface hoar combo found down 50 - 100cm is largely unreactive.
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.