Regions
South Coast Inland.
Give cornices a respectful berth.
Confidence
Moderate - Intensity of incoming weather systems is uncertain
Weather Forecast
THURSDAY: 10-20 cm snow. Moderate to strong southerly winds. Freezing level near 1500 m.FRIDAY: Light snow. Light southerly winds. Freezing level near 1700 m.SATURDAY: Light to moderate snow. Light winds. Freezing level rising to 1850 m.Weather models disagree on the amount of snow expected this week.
Avalanche Summary
A skier remotely triggered a size 2 slab on a NE aspect at 2100 m on Tuesday. It failed on facets. Watch for new storm slabs and wind slabs forming on Thursday. Storm slabs or cornice fall could potentially step down to a buried weak layer, creating a surprisingly large avalanche. New snow may sluff easily in steep terrain.
Snowpack Summary
Recent snow and moderate winds have created touchy slabs in specific terrain. Cornices are reported to be large and fragile. New snow overlies various old surfaces including melt freeze crusts on sunny aspects, scoured old hard wind slabs and dry snow.A weak layer consisting of surface hoar, facets or a sun crust buried in late March is now down about 60-80 cm. This is patchy in its distribution, but is mostly likely to be problematic on shady aspects between 1900m and 2250m. The mid and lower snowpack are strong and well settled.
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.