Regions
Northwest Coastal.
Updated weather models are indicating a southern shift of the storm, bringing unsettled conditions to the region. Nonetheless, over 100 cm of snow fell at high elevations with the storm, and rain below! The snowpack will need time to strengthen.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
WEDNESDAY NIGHT: Partly cloudy, light to moderate west winds, freezing level 500 m.THURSDAY: Mostly cloudy with light snowfall in the late afternoon, accumulation 5 cm, light to moderate east winds, alpine temperature -5 C, freezing level below valley bottom.FRIDAY: Mostly cloudy with light snowfall, accumulation 5 cm, light southwest winds, alpine temperature -4 C, freezing level 400 m.SATURDAY: Mostly cloudy with light snowfall, light to moderate southwest winds, alpine temperature -6 C, freezing level 300 m.
Avalanche Summary
It is expected that a natural storm cycle occurred from Monday to Wednesday morning with the substantial amount of new snowfall and rain. We are awaiting reports of what occurred. Nonetheless, the likelihood of avalanches is still elevated, particularly at high elevations where all the precipitation fell as snow.
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 1300 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. The thickest crust will exist below treeline.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.
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.