Regions
Northwest Coastal.
The ongoing storm continues and is driving the Danger Ratings. Deeply buried persistent weak layers have become overloaded.
Weather Forecast
Another frontal system over the North Coast will continue to bring moderate precipitation and rising freezing levels 800-1400 m on Thursday/ Friday. The weekend looks to get very warm and sunny.Thursday: Higher elevations could receive up to 30 cm. Rain at lower elevations. Ridgetop winds light gusting strong from the SW. Freezing levels 1300 m.Friday: Snow amounts 5-10 cm on the coast. Mix of sun and cloud inland and in northerly areas. Ridgetop winds moderate from the NE. Freezing levels rising to 900 m. Saturday: A mix of sun and cloud. Alpine temperatures near 4.0 degrees. Ridgetop winds light from the NE. Freezing levels near 1300 m.
Avalanche Summary
A widespread natural avalanche cycle up to size 4 occurred on Monday and Tuesday and will likely continue through the forecast period. Deep persistent weak layers became overloaded, initiating very-large avalanches. In shallower snowpack areas, storm slab avalanches have stepped down to the December facet/ depth hoar layer. With more precipitation and strong forecast winds, natural avalanche activity will likely persist.
Snowpack Summary
The recent storm has brought 70 cm or more too coastal regions (60-110 mm) forming thick storm slabs and wind slabs on leeward features. Cornices have grown large. At lower elevations the snowpack has become saturated and weak 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 -140 cm. The early February layer is down 150 - 240 cm. These layers have become overloaded and are failing in some places initiating very-large avalanches.
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.