Regions
Northwest Inland.
Heavy storm loading from snow and then rain will push the Avalanche Danger to HIGH. I'd wait this one out from a safe distance.
Confidence
Moderate - Intensity of incoming weather systems is uncertain on Tuesday
Weather Forecast
On Tuesday and Wednesday an intense Pacific frontal system will bring moderate to locally heavy moist snowfall (20-40cm on Tuesday/ ~ 10-20cm on Wednesday) to higher elevations. A dry ridge of high pressure will deliver mainly clear skies on Thursday. Ridgetop winds will be extreme for the southwest with the storm, and then become light on Thursday. The freezing level will climb from 1200m to about 1800m over the course of Tuesday, hover around 1300m on Wednesday, and then spike to about 3000m by Thursday.
Avalanche Summary
No new avalanches were reported on Sunday. Heavy storm loading will spark a new round of storm slab avalanche activity on Tuesday and Wednesday while heavy rain at lower elevations will encourage loose wet avalanche activity. If the near surface crust breaks down because of rain at treeline or in the alpine, deeper, more destructive persistent weak layers may come back to life.
Snowpack Summary
On Tuesday and Wednesday, moderate to locally heavy snowfall will form new storm slabs while rain at lower elevations will further saturate the snowpack. Extreme winds and progressive warming throughout the storm will encourage the formation of a slabby, "upside-down" upper snowpack. Cornice growth is also expected to be significant during the storm. New accumulations will overlie a widespread melt-freeze crust that formed as a result of last week's warm weather and more recent cooling. The warm temperatures and sun over the last week woke up deeply buried weak layers within the snowpack. This includes a weak crust/surface hoar layer which was buried down 20-30cm in the north of the region, a widespread crust/facet layer buried in early February down up to 1m, a lingering surface hoar layer from January down around a meter, and weak basal facets at the bottom of the snowpack. Cooling should dramatically limit the reactivity of these old layers; however, they may come back to life during future periods of warming, solar radiation or heavy storm loading.
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.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.