The new snow is on a steady stabilizing trend, but avalanche hazards will persist the longest in wind affected areas. Watch for solar exposure to rapidly undermine stability.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
Monday: A mix of sun and cloud. Light south winds. Freezing level to 1700 metres with alpine temperatures of -4.Tuesday: Mainly cloudy with scattered flurries and a trace to 5 cm of new snow. Light variable winds. Freezing level to 1700 metres with alpine temperatures of -4.Wednesday: Cloudy with sunny periods. Light to moderate east winds. Freezing level to 1900 metres with alpine temperatures of - 2.
Avalanche Summary
One 12-48 hour old Size 2.5 wind slab avalanche was reported on Friday. It occurred naturally on a steep, unsupported, north facing feature in the alpine.Several natural cornice falls up to size 3.5 were reported on Tuesday.
Snowpack Summary
Recent moderate to strong winds redistributed new snow from the past few days into wind slabs on a range of aspects in the alpine and at treeline. These wind slabs have developed above a mix of old surfaces that include melt-freeze crusts below about 1900 metres and on solar aspects in the alpine. Fragile new cornice growth also developed along ridgelines over the course of the week. Below the new snow, a number of storm snow and crust layers that formed over mid to late March appear to be well bonded. The February weak layers are now down about 120-150 cm and the deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack. These deep weak layers produced large avalanches with cornice falls and other heavy triggers in late March and early April. They remain a concern and may be more likely to fail on southerly aspects during periods of strong solar radiation.
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.