South Rockies

A Special Public Avalanche Warning applies to this region. Rapid warming is set to undermine stability throughout the region over the coming days. Our deep persistent slab problem is about to be tested.

Moderate -

Monday: A mix of sun and cloud. Winds light from the west. Freezing level to 3000 metres with alpine temperatures around +4.Tuesday: Sunny with cloudy periods. Winds light to moderate from the southwest. Freezing level to 3400 metres with alpine temperatures of +5Wednesday: A mix of sun and cloud. Strong southwest winds. Freezing level around 3500 metres with alpine temperatures of +5

Explosives control in the south of the region on Saturday yielded a few Size 1 results, limited to wind slabs in the upper snowpack. Friday's post-storm observations included reports of storm slab avalanches having run generally to Size 2 in our region and in the adjacent Waterton National Park over the course of the recent natural avalanche cycle. As for persistent slab activity during that cycle, one Size 3 was suspected to have run on a persistent weak layer while one Size 2 was reported to have run to ground. On Thursday there was a report of a Size 2.5 natural avalanche 50-120cm deep on a northwest 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. For Monday, warm temperatures can be expected to promote instability within wind slabs and storm slabs. As the warm temperatures persist, and especially if we don't experience refreezing overnight, the potential for deep persistent slab releases will rise steadily each day. Any avalanches releasing on a basal weakness will likely be large and very destructive.

Roughly 10 cm of new snow received late last week has been redistributed by strong southerly winds at upper elevations. Where it hasn't blown away, this new snow now lies above the 15-30 cm of moist snow that fell over the region on Thursday, which was mixed with periods of rain at lower elevations. Together, these more recent accumulations overlie the 90cm of low density storm snow that we received last weekend. Strong shifting winds redistributed this previous storm snow in exposed terrain, forming wind slabs over a variable old surface which includes wind affected surfaces, facets, and/or a rain crust below around 1500 m. The poor bond at the interface between this older storm snow and the previous surface is suspected to be improving slowly.In deeper areas, the snowpack appears to be well settled with only 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. In these areas the snowpack's weakness may reach a tipping point as temperatures rise over the coming days.