Regions
Northwest Inland.
Confidence
Fair - Timing or intensity of solar radiation is uncertain
Weather Forecast
Synopsis: Northwest flow gives way to a frontal system that barely brushes the region on Tuesday night/Wednesday.Monday: Chance of flurries, with significant breaks in the cloud giving daytime warming. Afternoon freezing level around 500 m. Winds light northwesterly.Tuesday: Flurries late in the day. Freezing level 500 m. Southerly ridgetop winds increasing to around 50 km/h.Wednesday: Around 5 cm new snow. Freezing level 500 m. Winds light southeasterly.
Avalanche Summary
On Saturday, a size 2 avalanche was triggered remotely on a south aspect at 1800 m. This avalanche ran on the new snow/crust interface about 40 cm below the surface. On Friday, a size 2 remote-triggered avalanche was reported from a west aspect at 1450 m, likely failing on the March 9th surface hoar layer down around 50 cm. Another human-triggered avalanche was reported on Friday from a north aspect slope.
Snowpack Summary
20-40 cm of recent storm snow rests on a variety of old snow surfaces, including crusts, previous wind slabs and surface hoar (buried March 9th). Warmer temperatures and recent winds have now set this new snow into a reactive slab. The March 9th surface hoar layer is reported to be very touchy and appears to exist at all elevations and on a variety of aspects. I suspect cornices have become well-developed and could easily become unstable with daytime heating. The mid 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.