New snow and strong winds are creating very dangerous avalanche conditions. Travel in avalanche terrain is not recommended. Large avalanches are likely.
A layer of weak facets (sugary snow) can be found down 50-100 cm near a crust layer that formed in early December. The rapid load from new snow and wind will likely overload this weak layer and produce very large, destructive avalanches. Cornices could also reach their breaking point, triggering very large persistent slab avalanches on slopes below.
15-35 cm of new snow is forecast to accumulate by Saturday afternoon. The new snow will likely form a widespread, touchy storm slab problem across elevations and aspects. Winds are forecast to be strong from the southwest. Anticipate larger, more reactive slabs in wind-drifted areas.
Heavy snowfall and extreme wind on Saturday
Friday night: Overcast, 5-10 cm of snow, moderate southeast winds becoming strong southwest in the alpine, treeline temperatures rising from -13 C to -11 C.
Saturday: Overcast, 10-20 cm of snow, with enhancement expected in areas near the Coquihalla, strong southwest winds with extreme gusts, treeline temperatures rising to -6 C in the afternoon, freezing level rising to 400 m.
Sunday: Decreasing cloudiness, flurries with trace accumulations overnight, light northeast winds, high treeline temperatures near -8 C.
Monday: Mix of sun and cloud, no snow expected, light west winds, high treeline temperatures near -11 C.
Natural avalanches releasing in the new snow are likely on Saturday. These storm slab avalanches are expected to be large, widespread, and very sensitive to human-triggers. Avalanches in the new snow have the potential to step-down to recently reactive weak layers, producing very large, destructive avalanches. Cornices may also reach their breaking point, triggering persistent slab avalanches on slopes below.
On Thursday, an operator in the north of the region observed a widespread, large natural avalanche cycle, releasing on the early December crust on southerly aspects at upper elevations. In the neighbouring Sea-to-Sky region, we received reports of two large (size 2-3) persistent slab avalanches on northwest and southwest aspects between 1700-1900 m. Notably, skiers remote-triggered these avalanches while traveling uphill. Several small (size 1-1.5) sympathetic avalanches also released on nearby terrain features during these close calls. There are valuable accounts and photos in this MIN report and this MIN report.
An intense storm is taking aim at the region, with 15-35 cm of new snow expected by Saturday afternoon. The new snow is falling on a mix of previous snow surfaces, including wind-scoured surfaces, wind-drifted snow, and preserved powder. Although storm slabs are expected to be widespread across aspects and elevations, extreme southwest winds will be a major contributor to the size and likelihood of Saturday's storm slab problem.
A primary layer of concern is a weak layer of facets (sugary snow) over a widespread crust that formed in early December (down 70-130 cm). On Thursday, this persistent slab problem produced a natural avalanche cycle in the north of the region and surprised several recreationists in the neighbouring Sea-to-Sky region with large, remotely-triggered avalanches. This problem is particularly hard to predict, tricky to manage, and will likely continue to surprise complacent backcountry travelers. Given recent natural, remote-triggered, and sympathetic avalanche activity, these conditions require wide, conservative terrain margins and disciplined backcountry travel techniques. Get more details and photos in our forecaster blog.
