Regions
Banff Yoho Kootenay.
Expect no overnight freeze for the next few days (freezing levels to 2800 m tonight and higher Thurs. night). Larger avalanches may occur with incoming hot weather - be mindful of terrain overhead. The hazard will quickly climb to HIGH on Thursday.
Weather Forecast
Freezing levels will rise to 3000m by tonight with no overnight recovery, rising through tomorrow to 3600m for Thursday night. Expect a mix of sun and showers with light to moderate SW wind for Thursday - Friday.
Snowpack Summary
Dry snow still exists on high north aspects. Moist surface snow and a variety of melt freeze crusts other aspects and elevations. Unsupportive isothermal conditions to 1900 m. A basal weakness remains at the bottom of the snow pack - reactive to large triggers but may wake up with the incoming warm weather, 2800 m freezing level, & solar input.
Avalanche Summary
Wind kept things cool most of the day, only some loose wet late to size 1.5 late in the day on S-W aspects in the alpine. This was caused by a combination of warm ambient air temperatures and rocks in the slope absorbing the sun's radiation and additionally heating the slope.
Problems
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
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.