Wind slab problems have been developing since Saturday's storm. Slabs may not be as widespread as they were a few days ago, but they still require careful terrain management to avoid.
Weather Forecast
Monday night: Increasing cloud with possible isolated flurries and trace of new snow. Light to moderate northwest winds.Tuesday: Cloudy with isolated flurries and a trace of new snow. Light southwest winds. Alpine high temperatures around -6 with a mild temperature inversion.Wednesday: Cloudy with increasing flurries bringing up to 5 cm of new snow before increasing overnight. Light to moderate southwest winds. Alpine high temperatures around -4.Thursday: Cloudy with continuing flurries bringing an uncertain 5-20 or more cm of new snow, continuing overnight. Moderate to strong southwest winds. Alpine high temperatures around -3 as freezing levels climb to about 1400 metres.
Avalanche Summary
Reports from Saturday and Sunday show an active couple of days for avalanches, with numerous, small (size 1) to large (size 2.5) storm slab avalanches occurring both naturally and with ski cutting and skier traffic. Activity was focused for the most part in steep, unsupported terrain on all aspects. One notable outlier was a large (size 2.5) persistent slab release that was skier triggered below ridgecrest on a southwest aspect in the Connaught Creek area in Glacier National Park.Reports from before the storm showed a steady declining trend in persistent slab avalanche activity. On Wednesday, reported persistent slab activity was limited to a size 2 deep release triggered by a skier in the far southwest of the region as they entered an open glade below a treed ridge on a southeast aspect at 2200 metres. Our recent storm loading and storm slab activity has failed to produce consistent reports of avalanches stepping down to this layer, suggesting that it may finally have reached dormancy.Looking forward, expect a decrease in natural avalanche activity while the potential for human triggering sees a more gradual decline.
Snowpack Summary
Saturday's storm brought about 25-35 cm of new snow on the surface, with some isolated areas receiving up to 50 cm. Below the new snow interface, which appears for the most part to be free of any weak surface hoar crystals, 10 to 20 cm of older low density snow sits above old wind slabs in the alpine, and in some isolated areas above small surface hoar.Avalanche activity on the 70-130 cm deep weak layer that formed during the dry spell in early December has greatly diminished over the last week. This layer is composed of weak facets, surface hoar, and a sun crust on steep south-facing slopes. It is believed to be trending toward a dormant state after the loading test brought by Saturday's storm failed to produce consistent reports of avalanches 'stepping down' to trigger it. Places that might still challenge this assumption of dormancy would be steep north and east facing slopes between 1900-2300 m and steep south-facing slopes in the alpine.The lower snowpack is generally strong and settled, with a crust that formed in late October near the bottom of the snowpack.
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.