Regions
Northwest Inland.
The ongoing storm could pack a punch and 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
Weather Forecast
As the warm front heads north the associated cold front will move across the region tonight bringing continued light precipitation, extreme to strong SW winds and lowering freezing levels.Monday night: Trace snow amounts. Ridgetop winds strong-extreme from the SW. Freezing levels falling to 900 m. Tuesday: A mix of sun and cloud with some flurries. Ridgetop winds strong from the SW. Freezing levels rising to 1000 m. Wednesday: Light precipitation. Ridgetop winds strong from the SW. Freezing levels near 1000 m.Thursday: Snow amounts 10-15 cm. Ridgetop winds generally light from the SW with strong gusts. Freezing levels 1200 m.
Avalanche Summary
No recent avalanche activity has been reported. A week ago, a steep rocky NE facing feature at 1900m released naturally resulting in a size 3 avalanche. The possibility for large avalanches appears to be still there, and the chance of one is likely to increase with anticipated warming, and/ or localized new loads including precipitation and strong winds on Tuesday.
Snowpack Summary
10-15 cm of new snow fell at upper elevations and up to 30 mm of rain below treeline. The new snow will add to the20 cm that fell last Thursday onto a variety of old snow surfaces consisting of surface hoar, facets and melt freeze crusts. Strong SW winds have likely built new wind slabs on leeward aspects and a poor bond may exist.Below treeline a spring-like snowpack exists including melt-freeze crusts and possibly 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. While it's been mostly dormant, I would not rule out the possibility of it reawakening if we see prolonged warming and/or intense sunshine and new load from snow and rain.
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.