There is some uncertainty if we will have sun all day, or if there may be a band of high cloud for most of the morning. Strong solar radiation may result in loose wet avalanches and natural cornice falls.
Confidence
Moderate - Timing or intensity of solar radiation is uncertain on Saturday
Weather Forecast
Mostly clear overnight with light westerly winds and freezing down to valley bottoms. On Saturday, a mix of sun and high cloud with light southwest winds and freezing levels rising to 1700 metres. Cloud and light precipitation developing by Sunday morning with freezing down to at least 1000 metres. On Sunday, cloudy with 5-8 cm of snow and freezing levels rising up to 1300 metres. Light snow and light winds continuing on Monday, before the next ridge of high pressure brings back the clear skies.
Avalanche Summary
No new reports of persistent slab avalanches. On Thursday there were numerous reports of new storm slab avalanches up to size 1.5 from various aspects at and above treeline. There was also some loose wet avalanche activity in the afternoon on Thursday when daytime warming weakened the new storm snow on solar aspects. 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.
Snowpack Summary
New storm slabs have developed 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. Expect loose wet avalanches and natural cornice falls during periods of strong solar radiation and/or daytime warming.
Problems
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.
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.