Continued new snow and wind will bump the alpine danger up to Considerable. Watch for natural cornice falls and remote triggering of wind slabs.
Confidence
Moderate - Intensity of incoming weather systems is uncertain on Thursday
Weather Forecast
Some moisture trapped in the south to north flow coming out of Washington State should bring 3-5 mm of precipitation (5-10 cm of snow at treeline) overnight, and another 5-7 mm of precipitation during the day on Thursday. Some of the western upslope areas may see enhanced snowfall. Winds are expected to be light from the southeast and alpine temperatures should remain around -5. High pressure with light winds and cooler air should move into the region from the north on Friday. Some flurries may continue on Friday and Saturday with periods of broken skies and alpine temperatures around -10.
Avalanche Summary
Natural cornice avalanches and natural and skier controlled wind slab avalanches up to size 1.5 have been reported. Most of these have been on northerly aspects in the lee of local winds. Winds have been generally easterly, but some areas have had locally more southerly winds due to terrain.
Snowpack Summary
10-25 cm of new snow is now sitting on the mix of surface hoar, near surface facets, and sun crust that was left behind after the recent clear and warm weather. Easterly winds have transported the new snow and some of the loose snow available into wind slabs at higher elevations. The new snow is reported to be loose and unconsolidated except where the wind slabs exist. Forecast warming with continued light snow may settle the storm snow into a cohesive slab. The mid and lower snowpack is generally well settled and strong.
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.
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.