Regions
Northwest Coastal.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
The next storm system is expected to reach the north coast on Saturday morning. Heavy precipitation and strong winds are expected for Saturday and Sunday. Conditions should be milder to the north of the region. A ridge of high pressure should build on Monday.Saturday: Precipitation 15-20mm, freezing levels am: 600m pm: 1200m, ridgetop wind 40-60 km/h S-SWSat. Night/Sunday: Precipitation 15-25mm, freezing levels am: 1200m pm: 500m, ridgetop wind 40-60 km/h S-SW in the morning, easing during the dayMonday: Light flurries, freezing levels am: 300m pm: 600m, ridgetop wind light SW
Avalanche Summary
Widespread natural avalanche activity up to size 4 was reported on Tuesday and Wednesday. Many very large events were reported with avalanches running full path. Natural activity has tapered off on Thursday but we received reports of explosive and human-triggered avalanches up to size 3. A remotely triggered size 3 avalanche occurred on the early Feb persistent weak layer. This was triggered from 150m away and was 50-200cm deep.
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. Snow below 1000-1200m has been wet and been through several melt-freeze cycles. 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.