Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain on Thursday
Weather Forecast
Thursday: Moderate to locally heavy snowfall / Strong southwest winds / Freezing level at 1000mFriday: Heavy snowfall / Strong southwest winds / Freezing level at 1200mSaturday: Moderate snowfall / Moderate southwest winds / Freezing level at 1100m
Avalanche Summary
Numerous size 2 natural slab avalanches were reported in the Coquihalla area on Tuesday. The occurred on a variety of aspect between 1300 and 1600m. With forecast snowfall, I would expect continued storm slab activity at all elevations with increasing destructive potential.
Snowpack Summary
Between 40 and 80cm of recent snowfall overlies a medley of old surfaces which include: weak surface facets, surface hoar, thin wind slabs, a scoured crust, or any combination thereof. Professionals are expressing particular concern for the combination of buried facets on a crust being unusually reactive at lower elevations. Reports of whumphing and widespread avalanche activity further indicate a poor bond between the new snow and these old surfaces. Strong to extreme winds are shifting the new snow into deeper, reactive wind slabs in exposed terrain. With forecast warming and more snow on the way, the reactivity and destructive potential of the new storm slab will likely increase.The mid and lower snowpack are generally strong and well-settled. Although basal facets and depth hoar are likely to exist in the north of the region, but triggering has become unlikely.
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.