Regions
Banff Yoho Kootenay.
The amount of overnight freeze and solar input will be key to the danger ratings Sunday. If it does not freeze, danger ratings will be higher than listed, especially at treeline and below. SH
Weather Forecast
Freezing levels are forecast to drop to valley bottom Sunday morning, with afternoon freezing levels to 2100m. The Banff/Sunshine region could see sunny periods, and the Northern regions should be mostly cloudy. Moderate to Strong W winds Sunday and trace amounts of precipitation.
Snowpack Summary
Rain below 2000-2200m Saturday. Up to 15cm high density snow amounts in the alpine Saturday. Treeline elevations are taking the brunt of the heat/rain as some areas below treeline are below threshold and the alpine stayed at or below freezing. The mid pack at treeline and above still has weaker basal facets and depth hoar as a concern.
Avalanche Summary
Many loose wet avalanches to size 2 at treeline and below were noted Saturday through the forecast region due to Friday's heat, and Saturday's rain.
Confidence
Freezing levels are uncertain on Sunday
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.
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.
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.