Rising temperatures may push the hazard higher than forecast. Use extreme caution traveling near, or under cornices
Confidence
Moderate - Freezing levels are uncertain on Thursday
Weather Forecast
A ridge of high pressure has established itself over BC and western Alberta bringing generally clear skies and warm daytime temperatures. Freezing levels should drop to valley bottom overnight and may rise as high as 3000 metres later in the week. Although there is some disagreement in forecast models, expect unusually high alpine temperatures for Thursday and Friday.
Avalanche Summary
Natural avalanche activity appears to have slowed down west of the divide but there have been reports of skier controlled wind slabs to size 1. On the eastern slope, no new avalanches have been reported but potential wind slab activity is still on the radar.
Snowpack Summary
New snow with wind during the weekend contributed to wind slabs forming in lee terrain at treeline and in the alpine. A melt freeze crust which formed during the 2nd week of February has been reported between 40and 70 cm., perhaps more deeply buried in the south of the region. This crust layer has also been reported with surface hoar in some places, for the most part on high and north facing terrain. This melt-freeze crust is a critical layer to keep track of. Rain and warm temperatures at lower elevations have created a 2 to 4cm rain crust, mostly on on south aspects below 1800 m. West of the divide, a layer of buried surface hoar has been reported around 45cm below the surface. The last storm accompanied by mod SW winds has encouraged cornice growth. These cornices are reported to be huge and unsupported. With warm weather and sun in the afternoon, these could become a significant hazard. New surface hoar growth is now being reported throughout the region.
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.