Regions
Northwest Coastal.
The ongoing storm will pack a punch and is driving the Danger Ratings. The snowpack does not typically handle rapid change well and deeply buried persistent weak layers may re-awaken.
Weather Forecast
As the warm front heads north the associated cold front will move across the region tonight bringing continued heavy-moderate precipitation, extreme to strong SW winds and lowering freezing levels.Monday night: Snow amounts up to 15 cm. Ridgetop winds strong-extreme from the SW. Freezing levels falling to 600 m. Tuesday: Snow amounts 10-15 cm. Ridgetop winds strong from the SW. Freezing levels rising to 800 m. Wednesday: Snow accumulations up to 30 cm. Ridgetop winds strong from the SW. Freezing levels near 700 m.Thursday: Moderate precipitation for coastal areas, and light inland. Ridgetop winds generally light from the SW with strong gusts. Freezing levels 1000 m.
Avalanche Summary
Expect a widespread natural avalanche cycle to continue at all elevations on Tuesday. It will take a couple of days before things start to settle out. Travel in avalanche terrain is not recommended.
Snowpack Summary
Up to 30 cm (25-35 mm) of new snow fell overnight Sunday at upper elevations forming new storm slabs. Strong southerly winds has transported the new snow building thick wind slabs on leeward features and potentially overloading persistent weak layers that exist lower in the snowpack. I suspect cornices have grown large. At lower elevations the snowpack will likely become saturated adding to the already spring-like isothermal conditions.Two persistent weak interfaces exist deeper in the snowpack. The early March layer can be found down 75 - 100cm and is composed of facets/surface hoar on shady aspects and facets/crust on southerly aspects. The early February crust/facet/surface hoar combo is down 150 - 200cm. This layer was responsible for a couple of unexpected large avalanches right at the end of March and the beginning of April. These layers should be on your radar and could become reactive with intense loading from rain/snow, warm temperatures and strong winds.
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.
Wet Slabs
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.