New snow and shifting wind directions may create wind slabs on a variety of aspects, including slopes that are generally windward.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
THURSDAY: Cloudy with flurries (5-10 cm snow possible). Light to moderate Southwesterly ridgetop winds. Freezing level around 1200m.FRIDAY: Mostly cloudy. Light Southwesterly ridgetop winds. Freezing level around 1200 m.SATURDAY: Sunny. Light southwesterly ridgetop winds. Freezing level around 1400m.
Avalanche Summary
Numerous skier triggered size 1 wind slabs were reported at Treeline and above on a variety of aspects near Whistler on Wednesday.
Snowpack Summary
15 cm of new snow with moderate to strong winds from a variety of directions have created fresh wind slabs in exposed terrain at treeline and above. Numerous crusts exist in the upper snowpack, especially on solar aspects. Cornices are large and remain a concern: Saturday's fatal accident near Lions Bay illustrates the danger of them breaking off, and the large avalanches they can trigger. Expect small loose dry avalanches in steep terrain where the new snow is sitting on a crust.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.