Regions
Banff Yoho Kootenay.
Triggering an avalanche is likely, and large natural avalanches are possible over the next couple of days due to warm temperatures, strong West winds and recent new snow. SH
Weather Forecast
A mix of sun and cloud Sunday, with westerly alpine winds reaching 125-150+km/h, and strongest around the Banff region. Temperatures will remain above zero at valley bottom and alpine temperatures will stay just below freezing. We don't expect any significant snow over the next 3 days.
Snowpack Summary
Snowpack tests continue to produce moderate to hard sudden results on the Dec. 18th interface/basal weakness which has become one and the same in most areas with less than 1m of snow. New snow (5-10cm in Banff area, 15cm at Sunshine, 15-20cm in Lake Louise), warming temperatures and strong W winds are creating wind slabs in lee areas.
Avalanche Summary
Numerous natural avalanches were reported today. Notably, the bowl above the Urs hole ice climb on Cascade Mountain had numerous natural avalanches, with one size 3 stepping down to the basal weakness. This was likely triggered by sun. Wind loading in other alpine areas which received more snow saw isolated avalanches to size 2 on lee aspects.
Confidence
Timing or intensity of solar radiation is uncertain on Sunday
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.
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.
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.