Give cornices a respectful berth.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
An unsettled westerly flow is expected to bring around 5-10 cm snow on Thursday, with moderate to strong winds and the freezing level around 1500 m. Snow showers linger on Friday before a ridge brings mixed sun and cloud on Saturday.
Avalanche Summary
No new avalanches were reported yesterday. Over the last week we have received many reports of cornice failure, including one that triggered what appears to be a size 3 persistent slab in the north Elk Valley.
Snowpack Summary
Large cornices overhang alpine slopes and threaten to trigger avalanches on slopes below. Deep and hard wind slabs can also be found in some areas. Below around 2200 m, a couple of crust layers are buried in the upper snowpack. Snow surfaces became moist up to around treeline with recent warm weather and have formed surface crusts in many areas. Deeply buried weak layers near the ground may remain sensitive to triggering from thin snowpack areas or with large loads such as cornice fall.
Problems
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.
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.