Regions
Northwest Inland.
The ongoing storm is driving the Danger Ratings. Persistent weak layers could possibly re-awaken, initiating large and destructive avalanches.
Confidence
Fair - Intensity of incoming weather systems is uncertain on Wednesday
Weather Forecast
Another frontal system is targeted for the North Coast Wednesday/ Thursday bringing light-moderate precipitation and freezing levels hovering around 800-1400 m.Tuesday night: Snow amounts 10 cm. Ridgetop winds strong from the SW. Freezing levels falling to valley bottom. Wednesday: Snow amounts 10 cm. Ridgetop winds strong from the SW. Freezing levels rising to 1100 m. Thursday: Snow accumulations up to 20 cm. Ridgetop winds light from the SW gusting strong. Freezing levels near 1300 m.Friday: Unsettled conditions follow the frontal system bringing light precipitation, light SW winds. An approaching upper ridge will gradually start to dry things out later in the day.
Avalanche Summary
A widespread natural avalanche cycle up to size 4 occurred on Monday. I suspect natural avalanches will continue through the forecast period, however size and magnitude may decrease with cooler temperatures.
Snowpack Summary
20-30 cm of new snow fell at upper elevations and up to 40 mm of rain below treeline. The new snow fell onto a variety of old snow surfaces consisting of surface hoar, facets and melt freeze crusts. Strong SW winds have likely built thick wind slabs on leeward aspects and a poor bond currently exists.At lower elevations (Some treeline and below treeline), the snowpack is moist and/ or wet, saturated and weak. Two persistent weak interfaces exist deeper in the snowpack. The early March layer can be found down 75 - 100cm. The early February crust/facet/surface hoar combo is down 150 - 200cm. Recently, these layers have become overloaded with the new load from snow, rain and warmer temperatures. They must remain on your radar.
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.