If you receive less than 20 cm of new storm snow, the danger rating in the alpine is more likely Considerable.
Confidence
Fair - Intensity of incoming weather is uncertain on Sunday
Weather Forecast
The South Rockies will see one more day under a complex weather scenario but the ridge will begin to take hold late tomorrow.Overnight Saturday/Sunday: Overnight will bring moderate precipitation amounts. A light north-easterly return flow is expected, due to a low pressure system developing along the cold front. This will bring moderate to possible locally heavy precipitation amounts during the day. Ridgetop winds will blow moderate from the NW. Alpine temperatures near -7 and freezing levels falling to valley bottom.Monday: Mainly dry, cooler conditions with clearing sunny skies. Ridgetop winds will be light from the South. Alpine temperatures near -7 and freezing levels around 1200 m.On Tuesday and Wednesday a deep upper low over the eastern Pacific will push more snow from southerly directions over the southern half of BC again.
Avalanche Summary
On Thursday reports indicate a size 2 skier triggered avalanche off of a windloaded ridgeline feature running on a layer of facetted crystals. A subsequent size 1 avalanche was triggered nearby. This was in the Three Sisters area just north of Fernie.On Friday loose wet avalanches occurred up to size 1.5 from steep terrain features below treeline.
Snowpack Summary
About 30cm of storm snow has fallen with generally lower amounts in the North Elk and Crowsnest areas. The new snow has been shifted onto lee slopes by strong west and southwest winds creating wind slabs. With additional forecast snow and strong winds, storm slabs, cornices and wind slabs will continue to build. Below treeline the snow surfaces became moist with rain and warmer temperatures. As freezing levels fall to valley bottom, a crust will develop and may host a poor bond to new snow.Mid and lower snowpack layers are generally well settled.
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.