Regions
Kootenay Boundary.
Weather Forecast
A fairly benign, spring-like weather pattern has set up through the forecast period. Monday: A surface ridge will remain as a weak warm front moves through the western parts of the region. Skies will be sunny with high scattered cloud and no significant precipitation. Ridgetop winds will be light from the West and high diurnal temperature swings will persist. Treeline temperatures near -3.0 and afternoon freezing levels may rise to 1600 m. Tuesday/Wednesday: Mostly sunny skies with a bit more cloud cover on Wednesday. Freezing levels will hover around 1700 m in the afternoon. Treeline temperatures steady -3.0 and ridgetop winds will stay light from the West.
Avalanche Summary
Late on Saturday an avalanche fatality occurred in the Hell Roaring riding area located in the eastern ranges of the region. We have very limited information as the investigation is ongoing. At this point it sounds like a size 3 machine triggered slab avalanche. Additionally a skier triggered slab avalanche size 1.5 occurred in the Whitewater area (outside the ski area boundary). This avalanche was triggered from the leeward side of a cross-loaded feature and ran on a buried crust around 1980 m on a North aspect. On Thursday, several size 1.5-2 avalanches were either deliberately ski-cut or accidentally triggered on a range of aspects at elevations from 1800 - 2100 m. All failures were on a crust, typically buried 20-40 cm down.
Snowpack Summary
Between 20 and 80 cm of recent storm snow is settling into a cohesive slab overlying a thick crust that exists up to ridge top. The crust appears to have gained some strength in most places, but may still host a poor bond above 1800 m. In some places, you may find an additional thinner crust within the top 60 cm snow. This has been reactive to skier triggers. A buried surface hoar layer sits approximately 80 cm below the surface and continues to fail in a sudden planar fashion when tested. In some places it may not be a concern due to the thick supportive crust that lies above it. However, it may be more susceptible to a trigger from a variable, thin snowpack area or a large trigger like a cornice fall or a snowmobiler.Large fragile cornices loom over many slopes. These may become weak and fail under the influence of the sunshine. Cornice fall can act as a large trigger on slopes below, and may trigger a deeper instability if it exists.
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.
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.