Regions
Banff Yoho Kootenay.
Back to winter for a few days . . . dry slab avalanche conditions exist at treeline and above. For those who have been hitting big lines recently, be aware that conditions have changed and fresh windslabs exist in many areas up high.
Weather Forecast
A cold front will cross the region on Tuesday, bringing strong winds, 5-10 cm of snow and falling temperatures. Expect treeline temperatures to reach -7, and up high it could hit as low as -15. Cold fronts are short and intense, so behind this the air mass will stabilize and clear. Wed, Thurs and Fri could be very nice days.
Snowpack Summary
20-30 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
Some windslab activity up to size 2 observed in alpine areas over the last 24-hours.
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.