Triggering lingering storm slabs and fresh wind slabs is possible on Sunday, mainly from steep, north-facing alpine terrain.
Weather Forecast
SUNDAY: Periods of snow – around 5-10 cm. The freezing level is around 1400 m. Winds are moderate from the W-SW. MONDAY: A mix of sun and cloud. The freezing level climbs to 1800 m and winds ease to light. TUESDAY: Mainly sunny. The freezing level is around 1800-2000 m and winds are light.
Avalanche Summary
On Friday there were numerous reports of skier-controlled avalanches up to size 1.5 from steep wind-loaded alpine terrain. There were also a few size 2-3 natural cornice releases. On Thursday, we had reports of storm slab avalanches up to size 2.5 in isolated steep unskiable terrain.
Snowpack Summary
Up to 40 cm of recent storm snow has accumulated with thin new wind slabs in lee terrain, and a possible sun crust on solar aspects. Moist snow was reported on solar aspects in the alpine, and up to at least 1800 metres on shaded aspects. There are several thin crusts in the upper snowpack on all but shaded north aspects. The late February persistent weak layer continues to be a concern for wide propagations in isolated terrain, however it may take a large trigger like a cornice fall to initiate an avalanche. Watch for recent storm snow releasing as loose wet avalanches on steep solar aspects during periods of strong solar radiation and/or daytime warming.
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.