Regions
Kootenay Boundary.
A small storm Friday might give some localized areas of concern, while a bigger storm for Sunday is likely to give more widespread avalanche concerns.
Confidence
Fair - Due to the number of field observations
Weather Forecast
Two storms: a little one on Friday then a bigger one with warming on Saturday night and into Sunday. Friday: expect around 5-10 cm new snow with freezing levels around 1400 m and moderate southerly winds. Saturday: a brief lull in the snow with maybe even the odd break in the clouds. Saturday night/Sunday: Expect 20-30 cm new snow, initially falling as snow, then around midday Sunday getting warm with freezing levels reaching around 2000 m. Strong southwest ridgetop winds.
Avalanche Summary
On Wednesday, explosive testing produced small (size 1.5) avalanches on S to SE aspects at 2200 m in steep rocky terrain that were suspected to step down to the early November crust.
Snowpack Summary
10-20 cm new snow has buried a prominent surface hoar layer above a thick rain crust that extends as high as 2100 m. High elevation north aspect slopes do not have the rain crust, but on these slopes, facets or buried surface hoar from earlier in the month may be lurking under dense storm slabs. Recent snowpack tests at 2050 m in a NW aspect in Kootenay Pass produced moderate sudden results down 35 cm under the late-November crust and down 79 cm on facets above the early-November crust. Meanwhile in the Southern Purcells, snowpack tests last weekend gave easy sudden planer results on well preserved surface hoar where it was found down 30 cm on high north aspects.
Problems
Loose Dry
Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
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.