Regions
Northwest Coastal.
The Avalanche Danger is forecast to increase throughout the day on Sunday as the storm intensifies.
Confidence
Fair - Intensity of incoming weather systems is uncertain on Sunday
Weather Forecast
A pacific moisture stream will intensify throughout Sunday and then ease slightly on Monday. Although there is some model disagreement in regards to snowfall amounts, up to 20cm can be expected on Sunday, with another 15cm possible on Monday. A mix of sun and cloud is forecast for Tuesday. Winds are expected to remain strong to extreme from the west/southwest. Freezing levels may spike to 1500m on Sunday, and then hover between 500m and 1000m on Monday and Tuesday.
Avalanche Summary
There was a surprisingly limited amount of reported natural avalanche activity given the amount of new snow and wind on Thursday and Friday. Size 1 soft slabs were reportedly sensitive to human triggering in high elevation lee terrain. That said, I'd remain cautious of steeper, high-consequence slopes as a release on recently buried surfaces could have nasty consequences. Looking forward, more wind and snow forecast for Sunday will likely spark a round of natural storm slab activity. New new snow will also add more stress to these recently buried weaknesses.
Snowpack Summary
By Friday morning up to 40cm of new snow fell with the highest accumulations occurring in the southwest of the region. The new snow and strong southwest winds have built dense slabs on exposed lee features, while loose powder can be found in sheltered terrain. More snow and wind on Sunday will add to this developing storm slab. The new snow overlies a variety of interfaces including old hard wind slabs, hard crusts, surface hoar, and/or surface facets. At the base of the snowpack, weak facets may be found, particularly on alpine slopes in the north of the region. Keep an eye out for cornices that could fail.
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.