Conditions are more complicated than meets the eye. Wind-drifted snow and a buried weak layer warrant a cautious approach and diligent decision making.
Strong southwest winds during the recent storm drifted the new snow into dense slabs on leeward terrain features. These wind slabs may remain possible to human trigger, particularly near ridge-crests and roll-overs. Cornices may be reaching their breaking point and have the potential to act as triggers on slopes below.
A layer of weak facets (sugary snow) can be found down 70-160 cm near a crust that formed in early December. It is more likely to human trigger this persistent slab in thick to thin areas at tree line elevations. The possibility for large remote-triggered avalanches warrants conservative terrain margins.
Sunday night: Clear, no new snow expected, light east winds becoming northwest in the alpine, low treeline temperatures near -14 C.
Monday: Sunny, no new snow expected, light northwest winds, high treeline temperatures near -10 C.
Tuesday: Increasing cloudiness, isolated afternoon flurries with trace accumulations, winds becoming southwest and increasing to strong, high treeline temperatures near -7 C.
Wednesday: Overcast, 5-15 cm of snow, strong southwest winds, treeline temperatures near -6 C, freezing level around 300 m.
On Saturday, operators reported numerous small to very large (size 1-3) avalanches releasing naturally in the storm snow across elevations and aspects. Although natural avalanche activity is tapering, avalanche conditions may remain primed for human-triggering on Sunday. 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.
Saturday's powerful storm brought 20-30 cm of new snow, with favored areas near the Coquihalla seeing upwards of 60 cm. Strong south winds have redistributed the new snow into dense wind slabs that may remain possible to trigger at upper elevations, especially where the new snow is poorly bonded with the old snow. The recent snow sits on a variety of snow surfaces, hard wind-scoured surfaces, preserved powder, and possible surface hoar in sheltered areas. Stay alert to changing slab conditions as you move into wind-exposed terrain, and monitor the bond of the new snow to the old snow surface.
A culprit weak layer of facets (sugary snow) can be found over a widespread crust that formed in early December (down 70-160 cm). This layer seems particularly reactive at treeline elevations between 1700-2100 m and in the north of the region in areas such as the Hurley. 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 and tricky to manage. Given the rapid load from new snow and wind along with recent avalanche activity, this persistent slab problem requires wide, conservative terrain margins and disciplined backcountry travel techniques. Get more details and photos in our forecaster blog.
