Warm overnight temperatures will keep cornices weak before colder temps set in and fresh wind slabs begin to build on Saturday afternoon.
Weather Forecast
Saturday: Mainly cloudy with flurries beginning in the late morning and up to 5 cm accumulating at higher elevations by the end of the day. Light to moderate southeast winds. Freezing level dropping to 1500 metres over the day with alpine temperatures from -1 to -3.Sunday: Mainly cloudy with scattered flurries bringing approximately 5 cm of new snow. Light south winds. Freezing level to 1700 metres with alpine temperatures of -3.Monday: Cloudy with sunny periods and isolated flurries with a trace of new snow. Light southeast winds. Freezing level to 1800 metres with alpine temperatures around -2.
Avalanche Summary
Early reports from Friday showed significant cornice activity in the Whistler area, with several natural Size 2 releases and one Size 3.5 that triggered a large slab avalanche with a roughly 2 metre deep crown fracture. One of the Size 2 releases also triggered a 100 cm deep slab. Other natural and explosives triggered cornices ranged from Size 2-3 and mainly entrained loose snow, but a few thinner slabs were also triggered.Reports from Thursday included observations of several explosives controlled cornice releases in the Whistler area. Sizes ranged from 1.5 to 2.5 and one release successfully triggered a 15-30 cm by 15 m slab below it. Wednesday's reports showed explosives triggered storm slabs reaching Size 1.5 in the Whistler area. Crown depths averaged 20 cm.
Snowpack Summary
Friday's warm temperatures and sunshine moistened surface snow on most aspects and elevations. Warm overnight temperatures will prevent if from refreezing into a solid crust. Below the surface, stormy weather over the beginning of the week brought about 30-40cm of accumulated snow to the Sea to Sky mountains, with this precipitation falling as rain below about 1400m. Strong southeast winds over the same time period created pockets of wind slab in the alpine and exposed features at treeline, in addition to building fragile new cornice growth. The recent snow has gradually formed a good bond to the 'Easter crust' that exists below it on south aspects at all elevations. The mid and lower snowpack are generally well settled and strong.
Problems
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.