Regions
Northwest Coastal.
Confidence
Fair - Intensity of incoming weather systems is uncertain
Weather Forecast
The next storm system hits the north coast on Thursday night or Friday morning. A bit of a break is expected for Friday night before the second system arrives Saturday morning. The second system is expected to be stronger and should last until Sunday night. The south of the region can expect greater snowfall amounts than the north. There is a fair amount of uncertainty regarding freezing levels.Thurs. Night/Friday: Snow 15-30cm, freezing levels up to ~1000m, ridgetop wind 20-40 km/h SWSaturday: Moderate to heavy snowfall, freezing levels up to ~1000m, ridgetop wind 40-60 km/h SE-SWSunday: Moderate to heavy snowfall, ridgetop wind 40-60 km/h SE-SW
Avalanche Summary
Widespread natural avalanche activity was reported on Wednesday. Avalanches up to size 3.5 are being reported across the region and one size 4 was reported at the north end of the region. Avalanches are running within the storm snow, on the March weak layer down 60-100cm, and also stepping down to the Feb weak layer which is typically down around 1.5m but may be as deep as 2.5m.
Snowpack Summary
Storm slabs continue to build. At the end of the last storm pulse, the storm slab was up to 1m thick in the north of the region, . The south of the region had less snowfall and the slab is roughly 60cm thick. These slabs generally sit on a weak layer which may consist of any of the following: hard wind slabs or wind-scoured slopes in exposed terrain, a thick layer of faceted snow on sheltered, shady slopes, isolated surface hoar on sheltered, shady slopes, and sun crust on steep solar aspects. Expect moist or wet snow below roughly 1000m elevation. The mid February weak layer of surface hoar or a crust/facet combo is typically buried over 1.5m deep. This layer continues to react in snowpack tests, primarily on sheltered north aspects at or below treeline. The weight of the new snow and rain has the potential to reactivate this layer resulting in large, destructive avalanches. Basal facets and/or depth hoar remain an isolated concern in shallow snowpack areas in the northern part of the region.
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.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.