Flurries and wind will sustain wind slab development, use caution transitioning into wind-affected terrain.
A continuing supply of snowfall will sustain wind slab development. Recent wind direction has varied from northwest to southwest, creating wind slabs on a variety of aspects in exposed alpine and treeline terrain. Where wind slabs sit over a crust, they may be more sensitive to triggering.
FRIDAY NIGHT: Flurries, 5-10 cm. Alpine low temperature -8 C. Southwest wind 30-40 km/hr. Freezing level 600 m.
SATURDAY: Cloudy with isolated flurries, 5-10 cm. Alpine high temperature -3 C. Southwest wind 25-40 km/hr. Freezing level rising to 1200 m.
SUNDAY: Cloudy with isolated flurries, trace accumulation. Alpine high temperature -7 C. West wind 15 gusting to 50 km/hr. Freezing level 600 m.
MONDAY: Mix of sun and cloud. Alpine high temperature -7 C. Northwest wind 15-25 km/hr. Freezing level 800 m.
On Thursday, large cornices were reactive to explosives and skiers, and one failed naturally. Explosives triggered wind slab avalanches to size 1.5, which failed over a crust.
On Wednesday, a few natural loose wet size 1 avalanches were observed on steep solar aspects. Natural wind slab avalanches up to size 2 were observed on steep, north to east facing alpine terrain on Tuesday. A few skier triggered avalanches; wind slab size 1 and a cornice size 2 were reported on Monday and Tuesday. Most were triggered on north to east aspects in the alpine, but one slid on the rain crust on a south aspect at treeline.
A very large (size 3.5) avalanche was observed on Sunday near Whistler on a steep north face at 2400 m. It is suspected to have failed on a layer of facets on a crust from late November. This very large event demonstrates the ongoing need for caution in aggressive alpine terrain.
A bit of new snow and wind will further wind slab development in lee features at alpine and upper treeline elevations. This dusting of new snow overlies a variable surface of harder wind slabs, a sun crust of solar aspects, and settled snow in sheltered terrain. A rain crust sits 30-50 cm below the surface at elevations below 2000 m. The bond at this interface appears to be reasonably strong.
While weak faceted grains and crusts near the base of the snowpack have mostly not been a problem recently, a very large avalanche was observed on this layer on Feb 9. The problem appears isolated to very aggressive alpine terrain and is likely more prevalent in inland parts of the region.
