Avalanche Forecast

Moderate - Due to the number and quality of field observations

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.

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.

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.