Wind slab and cornice hazards remain a real concern. Careful evaluation of terrain, overhead hazards, and wind loading patterns is essential to safe travel.
Weather Forecast
Tuesday: Cloudy with light flurries increasing over the day and bringing 5-10 cm of new snow by Wednesday morning. Mainly light southwest winds becoming strong at higher elevations. Freezing level returning to the surface as the alpine temperature inversion breaks down. Alpine high temperatures around -2.Wednesday: A mix of sun and cloud. Light north winds. Freezing level rising to 700 metres with alpine temperatures of -7.Thursday: Mainly cloudy with light flurries increasing over the day and bringing 10-15 cm of new snow by Friday morning. Light southwest winds increasing overnight. Freezing level to 500 metres with alpine high temperatures of -8.
Avalanche Summary
We have a preliminary report of a snowmobiler that was fatally involved in a cornice failure in the Callaghan area on Saturday. Our understanding is that the individual was parked on or near the cornice when it failed beneath them. This failure resulted in a long fall from ridgetop and the partial burial of the individual in the debris.Reports from Sunday included one observation of a recent natural size 2 cornice release in the Spearhead Range as well as one explosives-triggered size 2 cornice. Warm temperatures and solar exposure caused one natural size 2 loose wet avalanche on a steep alpine slope in the Whistler area.On Saturday, two skier-triggered wind slabs were reported: a size 1.5 wind slab from a cross-loaded feature on a northwest aspect at 1900 m, and a size 2 on a north aspect at 2350 m, both near Whistler.On Friday, evidence of a natural cycle which likely occurred near the end of the warming period earlier in the week was reported, with storm slab activity up to size 3 observed on north to east aspects in the Mt Currie area.
Snowpack Summary
Highly variable snow surfaces exist. On south-facing alpine slopes, you're likely to find scoured crusty surfaces, while reactive wind slabs have built on lee slopes facing roughly north. More recent northerly winds have expanded wind slab formation to a range of other aspects. A melt-freeze crust has formed up to about 1900 m.On average, 180 cm of settled snow now sits on the mid-January crust which generally shows signs of bonding to the overlying snow; however, it has the potential to wake up with a large trigger such as a cornice fall. Below this, the snowpack is thought to be generally strong and well-settled.
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.