Regions
Kootenay Boundary.
Areas with accumulations of 30cm or more new snow are likely to see natural avalanches. These avalanches could be large and run far with crowns up to 1 metre deep. Even without natural avalanches, conditions are primed for human-triggered slides.
Confidence
Moderate - Intensity of incoming weather systems is uncertain
Weather Forecast
SUNDAY NIGHT: Another 10 cm new snow adding to Saturday's 10 cm. Freezing level around 1000 m. Moderate southerly winds.MONDAY: Yet another 10 cm new snow. Freezing level rising, as high as 1500 m. Moderate southwesterly winds.TUESDAY: Continued snow with another 15 to 25 cm. Freezing level around 1500 m. Moderate to strong southwest winds.WEDNESDAY: Snow tapering off after another 10 cm Tuesday night. Freezing level steady near 1500 m. Moderate westerly winds.
Avalanche Summary
Although avalanche reports are sparse on Sunday at the time this forecast was published, if you read the Snowpack Discussion above you'll see I expect storm slab or persistent slab avalanches to start running with 30 or more cm of new snow forecast by Monday evening.
Snowpack Summary
Until today the primary concern was the layer below last week's storm snow accumulations; that would be the Dec 09 (date it was buried) layer of facets (sugary crystals), surface hoar (feathery crystals) and a sun crust on south aspects all about 60 cm deep. By the time Monday morning rolls in I expect two primary concerns: Dec which will be getting to 70 cm or more below the surface, as well as some storm & wind slab issues (say within 30 cm of the surface, deeper in wind loaded pockets). Although 10 or 15 cm of new snow daily often won't start a natural avalanche cycle, it looks to me that we're getting real close to tipping the balance. The Dec 09 layer, it's primed; recent "sudden" snowpack test results and remotely triggered avalanches indicate it remains a critical layer. If the forecast storms materialize I expect this layer to wake up on Monday or Tuesday.Lower in the snowpack, previous weak layers from November appear inactive. These deeper layers could possibly cause problems on cold (north facing) slopes at high elevations where the snowpack is thin, but in most places, this is unlikely.
Problems
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.
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.