A major storm will lead to a widespread avalanche cycle in the new snow with the potential to step-down and trigger deeper buried weak layer. Avoid avalanche terrain.
A layer of weak facets (sugary snow) can be found down 70-150 cm near a crust that formed in early December. Storm slabs in motion may step down to this layer and trigger large destructive avalanches. Also, it is more likely to human trigger this persistent slab in thick to thin areas at tree line elevations.
Large reactive storm slabs will develop with ongoing storm snow and strong southwesterly winds leading to a widespread natural avalanche cycle during the day.
A combination of two systems, one from the coast of Washington State and the other from the Gulf of Alaska, will spread precipitation to the South Coast ranges.
Tuesday night: Snow, 15 to 25 cm, strong to extreme southwesterly winds, low treeline temperature near -8 C with freezing level at 900 m.
Wednesday: Snow, 15 to 20 cm, strong to extreme southwesterly winds, high treeline temperature near -5 C with freezing level at 1200 m.
Thursday: Flurries, 5-10 cm, moderate to strong westerly winds, high treeline temperatures near -10 C with freezing level going back to valley bottom.
Friday: Flurries, 5 cm, light northerly winds, high treeline temperatures near -13 C with freezing level at valley bottom.
Although avalanche activity has momentarily tappered off on Monday and Tuesday, new storm snow and strong southwesterly winds will lead to another natural avalanche cycle on Wednesday. Storm slabs avalanches have the potential to step-down to recently reactive buried weak layers, with the potential to produce very large, destructive avalanches. Cornices may also reach their breaking point, triggering persistent slab avalanches on slopes below. Over the last few days, we received reports of large (size 2-3) avalanches from neighbouring Sea-to-Sky region that released on a persistent weak layer on northeast, northwest, southwest aspects between 1500-2100 m.
The ongoing storm have the potential to add 30 to 45 cm to the 30 to 50 cm layer of settling snow from last weekend's storm. All this new snow sits on a variety of snow surfaces, hard wind-scoured surfaces, preserved powder, and possible surface hoar in sheltered areas. Strong southerly winds will continue to redistribute the storm snow into dense wind slabs on leeward terrain features.
A culprit weak layer of facets (sugary snow) can be found over a widespread crust that formed in early December (down 70-150 cm). This layer seems particularly reactive at lower alpine and treeline elevations, between 1500-2100 m. Large size 2 and 3 avalanches on this persistent slab problem have been reported daily over the past few days in the neighbouring Sea-to-Sky region. This problem is particularly hard to predict and tricky to manage. Given the rapid load from the ongoing storm and wind, this persistent slab problem requires to scale back, adopt a conservative approach and avoid avalanche terrain. Get more details and photos in our forecaster blog.
