Avalanche Forecast

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

THURSDAY NIGHT: Mostly cloudy with light snowfall in the south of the region, accumulation 10 to 15 cm in the south of the region, light to moderate southwest winds, alpine temperature -5 C, freezing level below valley bottom.FRIDAY: Cloudy with light snowfall, accumulation 5 cm in the south of the region, light to moderate southwest winds, alpine temperature -5 C, freezing level below valley bottom.SATURDAY: Cloudy with light snowfall, accumulation 5 to 10 cm, light to moderate southwest winds, alpine temperature -6 C, freezing level below valley bottom.SUNDAY: Mostly cloudy, light northwest winds, alpine temperature -7 C, freezing level below valley bottom.

Reports indicate that a natural avalanche cycle occurred during the storm from Monday to Wednesday, with many large to very large avalanches (size 2 to 3.5) propagating widely and running far. For example, see the MIN reports here and here. Some of the avalanches, particularly in the north of the region, stepped down to the deeper weak layers described in the snowpack summary.

The snowpack varies substantially with elevation. Above around 1400 m, expect to find upwards of 100 cm of recent storm snow, which fell with strong southwest winds. The deepest amounts will be in lee terrain features adjacent to ridges. Below around 1400 m, the storm began with snow and switched to rain and may have switched back to snow again around treeline and upper below treeline elevations. With colder air temperatures, expect any wet snow to freeze and form a melt-freeze crust. New snow Thursday night will fall on these surface.In the northern part of the region, all this snow may overly a couple weak layers of feathery surface hoar buried near the end of December. Expect to find these layers about 50 to 120 cm deep.For most of the region around 150 to 200 cm deep, a weak layer of sugary faceted snow buried on December 8 may still exist. It is likely that this layer was the culprit of a large, remotely-triggered avalanche on December 30 near Terrace, described in a MIN report here. Other reports indicate that this layer is still present and it could be triggered by humans in shallow snowpack areas. Storm slabs could step down to this layer and produce very large avalanches.