Regions
Kootenay Boundary.
Touchy fresh wind slabs at higher elevations combined with lurking persistent weaknesses at lower elevations means you can't let your guard down this weekend.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
Saturday: Increasing cloud and snowfall throughout the day with 10-15cm possible by Sunday morning. Freezing levels in valley bottoms and light southwesterly becoming moderate to strong southerly ridgetop winds. Sunday: Another 5-10cm possible with freezing levels peaking at 1400m and moderate southerly easing to light southwesterly ridgetop winds. Monday: Mainly cloudy with light snowfall and cooler temperatures.
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.
Snowpack Summary
Recent heavy rain to treeline elevations and wet snow above 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 is surface hoar buried early December (now likely down 50-100cm), 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 weakness.
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.