Sunny weather returning after a brief storm. Watch for new storm slabs on dry shaded aspects and loose wet snow on solar aspects. Expect natural cornice falls due to sun and daytime warming.
Confidence
Moderate - Timing or intensity of solar radiation is uncertain
Weather Forecast
Snow ending overnight or early Friday morning, with cloud breaking up and becoming scattered in the afternoon. Periods of strong solar radiation with freezing levels climbing up to at least 1500 metres and light westerly winds. Expect a good freeze down close to valley bottoms on Saturday morning. Light southwest winds and mostly sunny skies during the day, high cloud developing in the late afternoon. Freezing levels climbing up to 1700 metres. On Sunday, expect mostly cloudy conditions with flurries or light snow by the afternoon.
Avalanche Summary
No new reports of persistent slab avalanches. On Wednesday we had reports of loose wet solar induced activity in most areas up to size to size 2.0, as well as some thin wind slabs in the high alpine on shaded aspects. I suspect that the new storm slab was reactive to human triggering on Thursday. New storm slabs may continue to be triggered on shaded aspects, and storm snow may release as loose wet avalanches on solar aspects.
Snowpack Summary
Forecast new snow and wind is expected to develop new storm slabs above a mix of surfaces, including crusts on solar aspects, moist snow up to treeline, and dry snow or recent wind slabs in the alpine on shaded aspects. Cornices continue to be described as large and fragile. The late February persistent weak layer is an aspect dependant mix of surface hoar, facets and/or a thick crust down around 60 to 110 cm below the snow surface. Commercial operators continue to see hard sudden planar results in snowpack tests, which suggests that wide fracture propagations are possible. New storm loading above the buried persistent weak layer may increase the likelihood of triggering large avalanches.
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.
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.
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.