Regions
Kootenay Boundary.
Confidence
Poor - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Two frontal systems will cross the region during the forecast period. The first is expected early Wednesday morning and the second is expected Wednesday night or early Thursday. Dry conditions are expected for Friday with some clearing. There is some uncertainty with the forecast freezing levels and freezing levels have the potential to be lower than those listed below.Wednesday: Rain or snow 10-15mm, freezing level around 2000m, ridgetop winds 20-40 km/h SWWed. Night/Thursday: Rain or snow 15-25mm, freezing level around 1400-1800m, ridgetop winds 30-50 km/h SWFriday: A mix of sun and cloud, mainly dry conditions, freezing level around 2000m, ridgetop winds light km/h SW-NW
Avalanche Summary
Explosive control on Monday produced numerous size 2 storm slab avalanches.
Snowpack Summary
20-30cm of new snow sits on top of surface hoar up to 10mm, near-surface facets, and/or a sun crust on south facing slopes. Warmer temperatures and the upcoming snowfall will likely result in the formation of a touchy, widespread storm slab. The immediate concern is deeper, wind-loaded areas where a cohesive slab already exists and immediate leeward features where stiffer wind slabs have formed during recently strong SW-W winds. A major concern remains a persistent slab (typical thickness 50-90cm) that sits below the new storm snow. This slab sits on a tricky weak layer consisting of facets, surface hoar, and/or sun crusts which was widespread at all elevations and aspects. While avalanche activity on this layer has decreased recently, reports suggest that where the layer still exists it has the potential to produce large, destructive avalanches. The phase we are now entering is referred to a 'low probability/high consequence' problem. It is possible that with the weight of the new snow, we may see a resurgence of natural activity on the 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.