Regions
South Coast Inland.
There is huge variation between the north and southern parts of the region. Cornices and deep weak layers remain a concern in the north.
Confidence
Moderate - Due to the number and quality of field observations
Weather Forecast
MONDAY: Overcast with flurries depositing trace to 10 cm of snow at treeline elevation, depending where you are in the region (Coquihalla gets the most, less to the north). Alpine temperatures near freezing with freezing level near 1200m. Wind moderate from the SW. TUESDAY: Cloudy with sunny periods. Isolated flurries but only a trace of precip. Alpine temperatures a few degrees either side of freezing with freezing level near 1500m. Wind light from the east. WEDNESDAY: Next system approaches bringing clouds, snow, and strong gusty SE winds. Freezing level near 1600m.
Avalanche Summary
On Saturday there was an accidentally triggered size 1.5 wind slab reported in the Whistler backcountry. I think this kind of shallow wind slab in alpine terrain is representative of a lingering wind slab concern: localized pockets, lee and cross-loaded features, around 20 to 30 cm thick. Saturday's fatal avalanche accident on Mt. Harvey, although not in the South Coast Inland region, does highlight several of the risks posed by cornices: multi-ton snow boulders serve as large triggers potentially releasing large avalanches on the slopes below, they can break well back making for tricky travel along ridge crests. It's all the more tricky when visibility is obscured in fog or heavy snow, if the easiest pathway (flat, hard snow, open straight line) is within the danger zone, or when they're so big that you need to be 10 or 15 or more metres back from the edge to remain safe.
Snowpack Summary
Anywhere from 15-25cm of new snow is sitting on a widespread melt-freeze crust that exists on all aspects and elevations except for high elevation north facing terrain. Recent moderate winds from the south have formed new wind slabs in the alpine and have added load to cornices. On sun exposed slopes and at lower elevations, several crusts likely exist in the upper snowpack which are generally well bonded. Both the mid February persistent weak layers and November deep persistent weak layer seemed to have become reactive to heavy loads (cornice falls and/or large explosives triggers) earlier in the week at upper elevations in the northern part of the region near Duffey and Birkenhead Lakes.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.