Touchy wind slabs in the alpine are sensitive to human triggering. Down in the valley, daytime warming and sunshine will break down the surface crust and raise the danger level.
Weather Forecast
Cloudy with sunny periods today, with light W alpine winds and freezing levels rising to 1900m. Monday will see much of the same with some isolated flurries resulting from the unstable air mass over BC.
Snowpack Summary
10-15cm of new snow at treeline. Settling storm snow in the top 60cm overlies a series of crusts on most aspects up to 1900m. Moderate SW winds at tree-line and alpine have formed wind slabs on lee features. Cold, dry snow can be found on northerly slopes while solar aspects rapidly become moist with sunshine. Huge cornices line the upper ridges.
Avalanche Summary
A field team encountered touchy surface wind slabs in northerly lee aspects at 2200m yesterday. The 10-15cm soft slabs were easily failing with ski cuts and running fast on a temp crust. On Friday, several large avalanches from Mt Macdonald to size 3.5 were observed running to the valley floor, likely cornice triggered.
Confidence
Timing or intensity of solar radiation is uncertain
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.