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
Nothing too crazy for the weekend: slightly warmer than seasonal temperatures and only a few flurries are expected. Clear fine weather for early next week. SATURDAY: Mainly cloudy with the possibility of isolated flurries (local accumulations 5-10cm), light south wind. Freezing level dropping to 1000m and alpine high temperatures to -4 Celsius.SUNDAY: Flurries with another 5-10 cm possible, moderate southerly winds. Freezing levels remaining around 1000m and alpine high temps to -4 Celsius.MONDAY: Cloudy with sunny breaks. Light northerly wind and freezing level around 700m, alpine high temperatures to -3 Celsius.
Avalanche Summary
Conditions are touchy in some sections of the Rossland range: On Thursday there was a skier triggered size 2 with a full burial, running on the mid November crust, west aspect near 2000m. On Thursday several natural, explosive and human triggered storm slabs were reported primarily on northerly aspects at treeline and alpine elevations. Expect lingering human-triggered avalanche potential for the forecast period. Also, expect deeper persistent weaknesses (basal facets, mid-November rain crust, mid December surface hoar / facets) to become more reactive with the new snow, wind-loading and warm temperatures. Time to dial back the terrain use!
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.