A Special Public Avalanche Warning applies to this region. Don't let your guard down yet. A combo of recent snow, strong winds, and rising temperatures will keep avalanche danger elevated through the weekend.
Confidence
Moderate - Freezing levels are uncertain on Sunday
Weather Forecast
Friday night: Flurries bringing up to 5 cm of new snow. Winds extreme from the southwest.Saturday: A mix of sun and cloud. Winds strong from the west. Freezing level rising 700 metres with alpine temperatures of -11.Sunday: Mainly cloudy. Winds strong from the southwest. Freezing level rising to 800 metres with alpine temperatures of -5. Possibility of freezing level rising to 2000 metres with alpine temperatures above freezing.Monday: Cloudy with sunny periods. Winds light from the southwest. Freezing level rising to 1700 metres, possibly as high as 2500 metres, with alpine temperatures to -1 or possibly well above 0.
Avalanche Summary
On Thursday there was a report of a Size 2.5 natural avalanche 50-120cm deep on a NW aspect in Waterton Park. Nearby on the east slope of the Rockies, a Size 2.5 wind slab was brought down with explosives, leaving behind a 40-100cm crown fracture. Expect the recent dense storm slab to remain reactive to human triggering in the coming days as the all the new snow from the past 10 days starts to settle. Storm slab avalanches have the potential to step down to the basal weakness which would drastically increase the size and destructive potential of a resulting avalanche.
Snowpack Summary
15-30cm of moist new snow fell over the region on Thursday, with some periods of rain observed at lower elevations. This precipitation has accumulated above the 90cm of low density storm snow that we received last weekend. Strong shifting winds have redistributed the previous storm's snow in exposed terrain forming touchy wind slabs. These wind slabs are now obscured by the latest blanket of snow. All of this overlies a highly variable old surface which may include wind affected surfaces, facets, and/or a rain crust below around 1500 m. Recent reports suggest a poor bond between the storms' snow and the old surface. In deeper areas, the snowpack appears to be well settled with isolated concerns about the mid-December facet layer which was buried 50-100 cm deep prior to the weekend storm. In shallow snowpack areas and at lower elevations, the snowpack is weak, faceted, and has no structure. Prior to the storm, it was possible to step onto the snow surface in these areas and sink right to the ground.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.