Regions
Banff Yoho Kootenay.
Although we have switched to 'Spring Conditions", the recent series of storms have brought back more winter-like avalanche problems. Give the "big lines" a rest and assess the local stability from smaller terrain before committing to bigger terrain!
Weather Forecast
A fast moving system will drop 5-10 cm Tuesday night. Wednesday through Friday we should see a mix of sun and cloud with minimal precipitation and cool temperatures. The big story this week will be the wind, with moderate to strong W/ NW winds starting Wednesday PM which will cause further windslab development.
Snowpack Summary
30-50 cm of recent storm snow has been blown into windslabs in many areas at treeline and above. Although the cloud cover has kept the sun effect to a minimum, these windslabs are expected to be a problem in leeward areas for a few days. This overlies crusts in most areas, which appear to be providing some strength over the deep facet layers.
Avalanche Summary
A very close call yesterday with a solo skier triggering a size 2 windslab avalanche on a N aspect in the alpine on Cathedral mountain. The skier went for a ~300m ride and was partially buried with some gear broken. He was lucky to walk away with minor injuries. This is indicative of the windslab problem that has formed over the last few days
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.