Regions
Banff Yoho Kootenay.
Friday is a day to be careful. Not HIGH by definition, but it could be a hot day and if so avalanches will run. The snowpack is poor - today we experienced a frightening whumph and crack on a steep north facing slope. Things have not improved much.
Weather Forecast
Blue skies, sunshine and warm temperatures forecast for Friday, with strong winds at higher elevations (possibly) keeping things a bit cool (but don't count on it). Freezing levels may reach 2000m - sheltered, sun exposed places will be like a convection oven on Friday.
Snowpack Summary
The snow surface is a mix of surface hoar, suncrust and wind effected snow that overlies a generally weak snowpack. Shallow areas are very weak and today we observed a large whumph and crack propagation on a 35 degree N facing slope in the alpine. There are two weak layers in the mid-pack (Jan 6 and Feb 11) which present additional instability.
Avalanche Summary
Some wet loose snow avalanches were observed today in sheltered alpine bowls. On Wednesday a large slab was triggered by a cornice up high on the Wapta. On Tuesday a small sluff ran over the French Reality Ice Climb in Kootenay and triggered a 100 cm deep slab on the slope below.
Confidence
Timing or intensity of solar radiation is uncertain on Friday
Problems
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.
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.