Confidence
Fair - Intensity of incoming weather is uncertain
Weather Forecast
Saturday night: 10-25cm further snow, with the freezing level near 1200m. Strong winds. Sunday: 10-25cm snow. Strong to gale westerly winds. Freezing level around 1200m.Monday: Light snow. Light to moderate westerly winds.Tuesday: A few flurries, with sunny breaks. Gusty westerly winds.
Avalanche Summary
Natural avalanches were observed below 1500m on Friday, failing on the crust/facet combo. On Thursday, a skier remotely triggered a size 1.5 slab on a convex feature. It failed on facets beneath the storm snow. On Wednesday, three size 3.5 natural avalanches ran full path. A few other natural avalanches, up to size 2, were observed in steep lee (wind-loaded) terrain. I expect more avalanche activity to occur during the weekend's storm.
Snowpack Summary
Up to 1m of snow has fallen since Monday. Strong winds have created hard slabs, soft slabs and fragile cornices. Key concerns as further snow builds this weekend include a weak facet layer that was created during the brutal cold snap in mid-January and a buried crust, with associated facets, which is found below about 1500m and is quite touchy in some areas. Snowpack test results on this layer range from no result to easy, sudden shears.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.
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.