The quick change from stormy weather to clear sunny skies with high freezing levels is a concern for natural avalanches. This is not the time for big objectives.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Friday
Weather Forecast
Overnight: 5-10 cm of new snow with freezing down to 1300 metres by morning. Friday: Clearing in the morning, with strong solar in the afternoon. Daytime freezing rising up to 2200 metres with light southwest winds. Saturday: Little or no re-freeze below 2200 metres. Mix of sun and cloud with flurries developing in the afternoon. Sunday: Overcast with light snow and light winds. Daytime freezing levels around 1800 metres.
Avalanche Summary
Numerous storm slab and loose wet avalanches were reported from the Fernie area on Thursday. One natural cornice fall was size 3.0, and pulled a storm slab from the slope below. Our uncertainty revolves around whether the snowpack will get a chance to re-freeze in the morning before the sun starts to heat the snowpack. I think there is a good chance that storm slabs will continue to be reactive, and strong solar may release cornices and storm slabs as daytime temperatures and freezing levels climb.
Snowpack Summary
Storm slabs continue to grow at higher elevations. Another 10-15 cm by Thursday morning has made the recent storm total near Fernie 50-70 cm. In the Corbin area, there was a total of 25cm on Wednesday. Storm snow is not bonding well to crusts in the alpine and at treeline. Below 1800 metres the snow is moist or wet. The recent storm snow may be sitting on a crust that developed just before the new snow arrived. This crust may act as a smooth sliding surface when the sun heats the storm slab. Deeply buried facets may spring to life due to the added load of the storm slabs, and the possibility of strong solar radiation over the next couple of days.
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
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.