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 avalanches reported. On Tuesday, we had a report of a natural slab avalanche size 2.5 on a southwest aspect at 2200 metres with a wide propagation and depth of about 100 cm, the bed surface was sun-crust with melted surface hoar on top. Solar induced loose wet avalanches up to size 2.0 were reported on Monday and Tuesday.
Snowpack Summary
Forecast new snow and wind is expected to develop new storm slabs at all elevations. Daytime warming continues to melt surface snow, and overnight crust recovery has been variable depending on cloud cover. Large cornices loom over many ridge lines and many are teetering on the brink of failure. Old wind slabs may remain a problem on high elevation north facing features. The make up of the late February persistent weak layer is an aspect dependant mix of surface hoar, facets and/or a thick crust down around 70 to 100 cm below the snow surface. Large triggers like natural cornice fall and explosive control work continue to initiate avalanches failing on this interface. The recent warm to cool temperatures should give the overlying slab a bit of strength, but it has yet to prove itself trustworthy. Unfortunately there's not much of a reliable pattern telling us what exact aspects are most suspect. As a precautionary measure, we recommend remaining suspicious of steep unsupported features at and above treeline.
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.