Regions
Kootenay Boundary.
Touchy fresh wind and storm slabs at higher elevations combined with lurking persistent weaknesses at lower elevations means you can't let your guard down this weekend.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
The last Pacific storm system is expected to hit the region Saturday overnight. 10-15cm of snowfall is expected with freezing levels around 1000m or so. Light scattered snowfall may continue through the day on Sunday. Alpine winds are expected be strong from the SW in the morning but will ease in the afternoon. Monday is expected to be dry with a mix of sun and cloud. Freezing levels are forecast to drop to near valley bottom and alpine winds should be light from the NW. Tuesday looks to be similar with mainly dry condition and a mix of sun and cloud.
Avalanche Summary
Reports from Thursday include an explosives-triggered 50cm thick persistent slab avalanche running on the early-December surface hoar on a convex roll below treeline in the Monashees. No new avalanches were reported on Friday.
Snowpack Summary
Recent heavy rain to treeline elevations and wet snow at higher elevations has saturated and loaded the upper snowpack, forming a thick crust which now has up to 20-25cm of fresh snow on top (with perhaps a thin crust within it). Weaknesses linger within the recent snow as well as at deeper old snow surface interfaces, which consists of facets, surface hoar, and/or a crust at upper elevations (especially on southerly aspects). The most critical of these weak layers is surface hoar buried early December (now down 70-100cm), which has the potential for remote triggering, extensive releases and prolonged sensitivity to triggers. It is likely lurking in most sheltered areas treeline and below. The thick mid-November crust is just under this weak surface hoar layer.
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.