Regions
Kootenay Boundary.
In the southwest corner of the region there's an unusually weak snowpack. Conditions are primed for people triggering avalanches. Don't let the lure of deep powder draw you into terrain that's inappropriate for the conditions.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
Some unsettled weather for Sunday and only a few flurries are expected. Clear fine weather for early next week.SUNDAY: Flurries with 5-10 cm possible, moderate southerly winds. Freezing levels remaining around 1200m and alpine high temps to -4 Celsius.MONDAY: Cloudy. Light northerly wind and freezing level around 1100m, alpine high temperatures to -5 Celsius.TUESDAY: Cloudy with sunny breaks. Light northerly wind and freezing level around 900m, alpine high temperatures to -8 Celsius.
Avalanche Summary
We had a great MIN report of a cornice-triggered Size 2 on Friday near Cabin Peak in the Bonnington range. The initial failure was in the storm slab on a southeast aspect near 2000m, which stepped down to trigger a weaker layer deeper in the snowpack.We also had a MIN report of a skier-triggered Size 2 on Thursday in the Rossland range. The failure was a deep persistent slab on a cross-loaded west-facing slope, possibly running on mid December facets or even the November rain crust / facet combination. Avalanche control in the eastern part of the region gave several Size 2.5 - 3 avalanches running within the storm slab layers on easterly aspects, and some gouging down to ground or into faceted layers deeper in the snowpack, and running full path.
Snowpack Summary
By Friday morning another 2-10 cm added to the previous 25-45 cm of fresh snow this week, accompanied by moderate to strong southerly winds. This has resulted in touchy storm and wind slabs bonding poorly to the previous snow surface that includes facets and large surface hoar on sheltered slopes and/or a sun crust on steep sun-exposed aspects, as well as wind-affected surfaces (e.g. hard wind slab, sastrugi, scoured crust, etc.) in exposed areas. In some areas of the Rossland range, the mid-November rain crust / facet layer is now likely down 50-90 cm and has become reactive with continued loading and warming. In thin rocky areas, particularly in the Rossland range, recent reports include easy sudden collapse snowpack test results on facets down 120-150 cm near the ground. This deep persistent weakness may also become reactive with continued loading and warming.
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.