Northwest Coastal

Significant amounts of new snow with extreme winds have set up touchy hard wind slabs in many areas that will stay reactive to human triggering for a while. There is a possibility of avalanches stepping down to lower layers in isolated spots.

Moderate - Wind effect is extremely variable

Friday: Dry and sunny. Light northeasterly winds. Alpine temperatures around -10C. Saturday: Dry and sunny. Light easterly winds. Alpine temperatures around -13C. Sunday: Dry and cloudy. Winds starting to increase during the day reaching 50 km/h from the south at ridgetop by the afternoon. Temperatures around -13C.

We're starting to get a bit of a picture that there was a reasonable natural avalanche cycle (as expected) up to size 3 that occurred during and immediately after the storm that ended on Wednesday. West of Terrace there was evidence of avalanches running in the storm snow up to size 3 on both north and south facing slopes. Storm slab avalanches up to size 2 had previously been reported on Sunday through Tuesday. I would anticipate wind slabs will remain touchy for a few more days, especially where they have formed into hard slabs in the alpine.

Up to 125 cm new snow was recorded in this region between 17 and 21 December. Winds were often extreme, and fresh hard wind slabs are reported to be widespread. All this new snow sits over a highly variable interface comprising of hard wind slabs in wind exposed terrain, widespread faceting of the upper snowpack, and 5-10 mm surface hoar in sheltered areas. The new snow was expected to bond poorly to this interface, but it's been notable how few avalanches have been reported, and the ones that have have been on the smaller side (typically size 2). Did the outflow winds scour the surface of any surface hoar before the new snow arrived? Has the upper snowpack remained soft preventing large slab avalanches? Is nobody out there looking because the storm has been so severe? In areas with less snow, there are two additional layers that should be on your radar. The first is a layer of surface hoar which was buried mid-November and may now be down around a metre in thinner spots. The second is an old rain crust from November that may have developed weak facets, particularly in the north of the region.