Regions
Kootenay Boundary.
Precipitation amounts are uncertain Monday night and Tuesday. This forecast is based on the upper end of predictions. Regardless how much snow falls, a persistent slab is primed for human triggering and a conservative approach is recommended.
Confidence
Low - Forecast snowfall amounts are uncertain on Tuesday
Weather Forecast
MONDAY NIGHT: Snow, accumulation 5-10 cm. Alpine temperature -3. Moderate southwest wind. Freezing level 1200 mTUESDAY: Snow, accumulation 10-20 cm. Alpine temperature -2. Moderate to strong southwest wind. Freezing level 1500 m.WEDNESDAY: Flurries, accumulation 5cm. Alpine temperature -3. Light west wind. Freezing level 1300 mTHURSDAY: Flurries. Alpine temperature -2. Moderate to strong southwest wind. Freezing level 1400 m.
Avalanche Summary
Recent reports indicate explosives controlled storm slab avalanches running to size 2 on Monday on southerly aspects at tree line and in the alpine. Expect to see the likelihood of triggering storm and persistent slab avalanches increase as new snow amounts begin to accumulate Monday night through Tuesday.
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. After the latest storm Monday night into Tuesday, the Dec 09 will be 70-80 cm below the surface, as well as some new 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 like 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 may wake up as we continue to build the load on top of it.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.