Regions
Northwest Coastal.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
The storm is expected to end on Sunday night. A break between storms is expected for most of Monday before the next system arrives Monday evening. The north of the region can expect less snowfall amounts than the south.Sat. Night/Sunday: Snowfall 20-40cm, freezing level am: 800m pm: 500m, ridgetop winds 30-50 km/h S-SW easing during the day.Monday: Cloudy with sunny breaks, mostly dry during the day, freezing level am: 300m pm: 600m, ridgetop winds 20-40 km/h W-NWMon. Night/Tuesday: Snow 15-25cm, freezing level am: 500m pm: 1000m, ridgetop winds 30-50 km/h SW
Avalanche Summary
Observations during the storm are limited but we have received reports of wind slab activity and explosive triggered slabs releasing on the early-March layer. Widespread natural activity is expected for Saturday night and Sunday.
Snowpack Summary
Storm slabs continue to build. S-SW winds are building wind slabs in leeward features. A widespread crust is expected below the storm snow at lower elevations.Before the weekend storm, the early March persistent weak layer was down up to 1m in the north of the region. The south of the region had less snowfall and the slab was down roughly 60cm. This weak layer consists 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. The early-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 around 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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
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.