Confidence
Fair - Intensity of incoming weather is uncertain
Weather Forecast
Saturday night: Light snow. Light W winds. Freezing level at the surface.Sunday: Light to moderate snow. Light NW winds with gusty N winds. Alpine temperature near -7.Monday: Light snow. Light W winds, gusting to strong NW winds. Alpine temperature near -6.Tuesday: Light snow. Light SW winds. Alpine temperature near -11.
Avalanche Summary
A widespread natural avalanche cycle was observed during the recent storm, including loose dry and soft slab avalanches at the beginning of the storm, and wet avalanches in areas where it warmed up. Skiers also triggered wind slabs on lee slopes. Most avalanches were in the size 1.5-3 range and failed within, or at the base of, the storm snow.
Snowpack Summary
The recent storm dropped anywhere from 40 cm to 1 m of snow at upper elevations, while rain soaked the snowpack below treeline. The storm snow was very reactive, creating big avalanches. The freezing level was between 1700 m and 2400 m during the storm, and lowered on Saturday, most likely forming a frozen crust in some areas. Strong NW through SW winds have redistributed snow into wind slabs and created cornices at alpine elevations. Below the storm snow is a layer of buried surface hoar and/or a crust. Deeper in the snowpack, a weak interface buried in mid-February is still on the radar. Although unlikely to be triggered, it remains possible with a very heavy load or from a thin-spot trigger point. A facet/crust layer sits at the base of the snowpack in some areas.As temperatures cool, wet slab/loose wet avalanche problems should improve, but persistent slab concerns at upper elevations may linger, especially on slopes which didn’t avalanche during the storm.
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.