Northwest Coastal

If more than 20 cm falls by Thursday morning, consider alpine danger to be High.

Fair - Forecast snowfall amounts are uncertain on Thursday

Wednesday night: 5 to 10 cm new snow with a little more possible in extreme coastal regions. Extreme wind speeds, gusting to 100km/h from the SW. Freezing level around 1000 m near the coast, a little lower inland.Thursday: continued snowfall, with around 10cm expected. Winds gusting to 60 km/h, initially SW'ly then becoming SE'ly. Freezing level around 500 m. Friday: Mostly dry, with partial clearing. Winds easing to light or moderate from the SW. Freezing level dropping to sea level. Saturday: Moderate or locally heavy snowfall amounts likely, with moderate SE'ly winds and freezing levels around 200 m.

On Tuesday, only one size one slab avalanche was reported from a north aspect at 1400 m. On Monday, avalanches up to size 2 were observed in the recent storm snow at all elevations. Although they appeared to only affect the top 10-20 cm of the snow surface, they were reported to be running far. Sluffing on steep terrain has also been reported. I suspect natural avalanche activity will ramp up overnight Wednesday and into Thursday with the incoming storm.

Recent storm snow amounts are much higher close to the coast compared with even a little way inland. The new snow was warmer and denser in places compared with the existing snow on the ground, helping to create touchy storm slab conditions. Winds marked a significant shift from mostly light northerly to a period of strong south southwesterly to southeasterly. These have set up touchy wind slabs in many exposed lee areas. There are two surface hoar layers in the upper snowpack. The upper one formed at the end of December and is buried approximately 30 cm below the surface. Professionals have reported easy, sudden planar compression test results on this layer and it has been reactive to skier-triggering. The lower one formed at the beginning of December and is buried approximately 90 cm below the surface. Hard, planar compression tests have been reported on this layer. Near the base of the snowpack, a crust/facet layer continues to give hard, sudden results to no results in snowpack tests. This weakness is unlikely to be triggered by a single person, but it remains possible with a very heavy load (e.g. cornice fall) or from a thin-spot trigger point.