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Avalanche Forecast

Archived

Dec 31st, 2018–Jan 1st, 2019

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.

Regions

Northwest Coastal.

Snowfall amounts are variable between models, but they all indicate that a powerful, multi-day storm is incoming. Expect an avalanche cycle if substantial snow and/or rain falls. Best to avoid avalanche terrain; avalanches may run full-path.

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

MONDAY NIGHT: Cloudy with heavy snowfall, accumulation 30 to 40 cm, strong southwest winds, freezing level rising to 1200 m by the morning.TUESDAY: Cloudy with light rainfall at lower elevations and otherwise snowfall ending near noon, accumulation 10 cm, strong southwest winds, alpine temperature 1 C, freezing level 1600 m.WEDNESDAY: Early-morning snowfall, accumulation 20 to 30 cm, then mix of sun and cloud, moderate to strong southwest winds, alpine temperature 0 C, freezing level 1400 m.THURSDAY: Cloudy with snowfall, accumulation 30 to 50 cm, strong south winds, alpine temperature -1 C, freezing level 900 m.

Avalanche Summary

On Sunday, a skier remotely triggered a large (size 3) avalanche in the backcountry near Shames. See the MIN report here, which describes it and there are also some photos floating around social media. Although unclear, it appears that the likely culprit was the mid-December weak surface hoar layer described in the snowpack summary.Further evidence of the storm cycle from the weekend was also noted.

Snowpack Summary

Up to 50 cm of new snow are possible in the region, with rain at lower elevations. The storm is incoming with strong southwest winds, which will produce wind slabs in lee terrain features. A pre-Christmas layer of surface hoar was previously buried on or around December 22, and will likely be buried anywhere from 50 to 150 cm below the surface. It is unclear how reactive this layer is, but its presence could increase the potential size of avalanches from the recent storm snow.Lower in the snowpack, sitting somewhere between 150 to 200 cm below the surface lies a weak layer from mid-December. It is likely that this layer was the culprit of a large, remotely-triggered avalanche on December 30 near Terrace. There are other reports indicating that this layer is still well-developed in the south of the region and it could be triggered by humans in shallow snowpack areas. For the north of the region, such as Ningunsaw, this layer was most prevalent between 1100 to 1300 m.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.