Northwest Coastal

Heavy storm loading has increased the avalanche danger, and buried weak layers exist in the snowpack. A conservative approach to mountain travel is critical.

Moderate - Intensity of incoming weather systems is uncertain on Tuesday

Tuesday: 5-15cm of new snow / Strong west winds / Freezing level at 600mWednesday: 20-40cm of new snow / Extreme Southwest winds / Freezing level at 1000mThursday: 5-10cm of new snow / Moderate southwest winds / Freezing level at 600m

Observations were highly limited on Monday, but I suspect there was an impressive natural avalanche cycle on Sunday night in response to heavy storm loading. More snow on Tuesday will promote ongoing storm slab activity at the surface. However, my bigger concern remains the buried weak layers below Sunday's storm snow. Large to very large avalanches at this interface remain possible and may be sensitive to human triggering or a surface avalanche in motion.

On Sunday night the region got pummeled by heavy snowfall and extreme westerly winds. By Monday morning, 24 hour totals were around 40cm around Bear Pass, and between 40 and 85 cm along the Hwy 16 corridor. The resulting deep storm slab sits over a highly variable interface resulting from over a week of clear skies, cold temperatures, and strong outflow winds. This mid-December interface consists of scoured surfaces and 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 is expected to bond poorly to this interface. A layer of surface hoar which was buried mid-November was down 50-80 cm in many parts of the region prior to the storm. This layer has been dormant recently but may increase in reactivity as the storm adds new load to the snowpack. In many areas in the region, the snowpack is reported to be very thin and faceting has been reported through the entire snowpack. In these areas, old rain crusts from November are developing weak facets. Concerns in the north of the region are basal weaknesses that may exist in the shallower snowpack areas.