Northwest Coastal

Rain, snow, and wind continue to load an already stressed snowpack. Stick to simple terrain and keep your distance from overhead hazards.

The storm continues through the weekend.   

Saturday night: Overcast, 10-20 cm of snow above 1500 m and rain below, strong southwest winds.

Sunday: Overcast, 10-20 cm of snow above 1400 m, strong southwest winds, freezing level dropping to 1300 m.

Monday: Mostly cloudy, 20-30 cm of snow above 1200 m, moderate southwest winds, freezing level dropping to 1000 m.

Tuesday: Mostly cloudy, 25-35 cm of snow above 1000 m, moderate southwest winds, freezing level dropping below 800 m. 

During the storm on Friday and Saturday, observers reported a natural cycle of large (size 2-2.5) slab avalanches releasing in the recent storm snow. One storm slab reportedly released from a corniced alpine ridge feature. Additionally, numerous small to large (size 1-2) wet loose avalanches were observed. 

In the aftermath of last weekend's storm, several very large deep persistent slab avalanches (size 3-3.5) that were both naturally and explosive-triggered released on an early November crust and weak snow at the ground. Easy-to-trigger wet loose or storm slab avalanches have the potential to step-down to these deeper layers and produce large, destructive avalanches.

Our eyes and ears in the mountains are limited this winter due to fewer professional observations. If you go out in the mountains, please share your observations on the Mountain Information Network (MIN). Photos are especially helpful! 

As of Saturday morning, weather stations had recorded 25-35 mm of water in 24 hours and above freezing temperatures up to 1900 m. At summit elevations and in areas further north in the region, precipitation fell as snow. Strong winds from the south have rapidly loaded areas receiving snow with touchy storm slabs. Ongoing snow and wind overnight and into Sunday will continue to build these touchy storm slabs and overload cornices. The new snow rests on a recent crust or hard, wind-packed snow that was buried earlier this week (Dec. 3). Below the freezing level, the snow surface is saturated. A gradual decrease in temperature will begin Sunday, bringing snow accumulations back down to 1400 m. 

The significant load from intense periods of precipitation has the potential to bring buried weak layers to their breaking point. Two early season weak layers are still on our radar. These consist of a layer of buried surface hoar that formed in late November and a facet/crust combination that formed in early November. Further north in the Ningunsaw and Bear Pass areas, weak snow developing near the ground has produced very large deep persistent slab avalanches. The extent of this snowpack structure in the region is not well-known, but it likely exists in colder, shallower areas in the region. 

The snowpack has settled rapidly given the above freezing temperatures and rain. Snowpack depths are highly variable across aspects and elevations as a product of wind scouring and freezing levels. Totals can range from roughly 100 to 250 cm at upper treeline and alpine elevations. 

• Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
• A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
• Avoid exposure to overhead avalanche terrain during periods of heavy loading from new snow, wind or rain.
• Storm slabs in motion may step down to deeper layers resulting in large avalanches.