Substantial amounts of snow may accumulate Thursday night into Friday. The snow will load a buried weak layer and may trigger an avalanche cycle. Best to avoid avalanche terrain on Friday and give the snowpack time to stabilize.
A touchy weak layer is buried in the snowpack, which may become more reactive with snow accumulation. This is an atypical snowpack for the region, which will require diligence until it strengthens. Avoidance of avalanche terrain is recommended for Friday, as large and destructive avalanches may fail on this layer.
Around 30 to 40 cm of snow may accumulate in the north of the region and 50 to 80 cm may accumulate in the south of the region over Thursday night and Friday. The snow will fall with associated strong southwest wind. A natural avalanche cycle may occur during the peak of the storm. Human-triggered avalanches are very likely to occur on Friday. Give this new snow some time to bond to underlying layers.
THURSDAY NIGHT: Cloudy with heavy snowfall, accumulation 30 to 50 cm, strong to extreme southwest wind, alpine temperature -4 C, freezing level 1200 m.
FRIDAY: Cloudy with snowfall, accumulation 5 cm in the north of the region and 30 cm in the south of the region, moderate to strong southwest wind, alpine temperature -5 C, freezing level 1100 m.
SATURDAY: Cloudy with snowfall, accumulation 5 to 10 cm, moderate southwest wind, alpine temperature -6 C, freezing level 900 m.
SUNDAY: Mix of sun and cloud, light south wind, alpine temperature -6 C, freezing level 800 m.
A natural avalanche cycle is possible Thursday night into Friday for areas that receive snowfall amounts of 30 cm or more. It will be best to avoid avalanche terrain during periods of heavy snowfall.
Around 30 to 80 cm of snow is expected to accumulate across the region by Friday afternoon, with the most in the south of the region (e.g., Coquihalla, Allison Pass). This snow will likely be very touchy and may produce both natural and skier-triggered avalanches Thursday night into Friday.
In the north of the region, the snow will load a weak layer of sugary faceted grains and hard melt-freeze crust buried mid-November, which is a recipe for large and destructive avalanches and a problem that may persist for weeks to months.
In the south of the region, the snow will load a weak layer of feathery surface hoar buried about 60 to 90 cm.
Avalanches triggered in the storm snow could step down to these buried weak layers, producing large and destructive avalanches.
