Regions
South Coast Inland.
The recent storm delivered a storm slab problem to the alpine while saturating lower elevations with rain. Be aware of increasing hazard as you transition to higher elevations.
Weather Forecast
Friday: Mainly cloudy with isolated flurries and a trace of new snow. Winds light to moderate from the south. Freezing level around 1400 metres with alpine temperatures of -6 in the north of the region, -1 in the south. Saturday: Mainly cloudy with isolated flurries and a trace of new snow in the south of the region. Scattered flurries bringing up to 5 cm to the north. Winds light to moderate from the south. Freezing level around 1000 metres with alpine temperatures of -6 in the north of the region, closer to 0 in the south. Sunday: Mainly cloudy with isolated flurries and a trace of new snow in the north of the region. Scattered flurries bringing up to 5 cm to the south. Winds light to moderate from the south. Freezing level around 1200 metres with alpine temperatures around -6 in the north of the region, closer to 0 in the south.
Avalanche Summary
Observations have been limited during the storm, but loose wet point releases were observes running to Size 2 at lower elevations north of Duffey Lake on Wednesday. A number of (presumably large) natural avalanches were also audible in the Bralorne area on Wednesday.
Snowpack Summary
In the Duffey Lake area 25 cm of snow fell on Tuesday through to Thursday morning. Elevations below 1900 m saw mainly rain. In the south (Coquihalla) we had moderate southerly winds and heavy rain above 1600m on Tuesday night (and rain to 2000m during the day Wednesday). This rain (or snow higher up) landed on either wind slabs in the alpine or temperature crusts at treeline and below, especially on east and south aspects. Both of these surfaces will be good sliding layers for future snowfall. The mid-December facets down 130-160 cm remain a concern especially in shallower snowpack areas in the Duffey, Hurley and/or South Chilcotins. These deeper weaknesses warrant renewed attention after considerable warming and extra loading this week. In southern areas (Coquihalla), the lower snowpack is reportedly well settled and stronger than it is to the north.
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.