Avalanche Forecast

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, heavy at times, 35 to 50 cm, strong to extreme southwesterly winds, low treeline temperatures near -5 C with freezing level rising to 700 m.

Wednesday: Snow, heavy at times, 35 to 55 cm, strong to extreme southerly winds, high treeline temperatures near -3 C with freezing level at 1000 m.

Thursday: Mainly cloudy with isolated flurries, 5 cm, light to moderate westerly winds, high treeline temperatures near -10 C with freezing level going down to valley bottom.

Friday: Mainly cloudy, light northerly winds, high treeline temperatures near -12 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 that released on a persistent weak layer on northeast, northwest, southwest aspects between 1500-2100 m, like in this MIN report.

The ongoing storm have the potential to add 70 to 100 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 100-200 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. 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. 

• Be aware of the potential for large avalanches due to the presence of a persistent slab.
• Avoid all avalanche terrain during periods of heavy snowfall.
• The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.
• Storm slabs in motion may step down to deeper layers resulting in large avalanches.