Snow, rain and wind combined with buried weak layers makes the perfect recipe for avalanches. Check out the new forecasters blog @ avalanche.ca.
Weather Forecast
Is spring the new winter? Waves of light, convective precipitation will continue overnight Friday and into Saturday. Amounts up 3-10 mm on Saturday, ridgetop winds moderate from the SW and freezing levels 2100 m then falling to valley bottom overnight. A dry day with a mix of sun and cloud is forecast on Sunday as the Pacific ridge crosses the province. Monday will see somewhat cooler temperatures with freezing levels near 1800 m and light precipitation 3-8 mm. Unsettled conditions will continue and progress as a series of fronts and ridges move across the region next week.
Avalanche Summary
On Thursday a skier controlled size 1.0 slab avalanche was reported. However, the snow and wind didn't start up in the Purcell region until Thursday afternoon. I suspect some natural avalanche activity occurred on Friday. A concern still exists for avalanches to step down to deeply buried weak layers, especially in shallower snowpack areas. With new snow, rain and strong winds natural avalanche activity will likely continue through the weekend.
Snowpack Summary
At higher elevations, 10-30 cm snow sits over a plethora of old surfaces including wind affected surfaces, and/or old wind slabs and crusts which were buried mid-March. Previous strong winds have redistributed new snow into wind slabs on leeward terrain features and lower elevations (below 2000 m) are sporting spring-like, melt-freeze conditions. Digging deeper (20-50 cm below the surface) sits the mid-February facet/ crust interface. This interface has not been reactive in the Purcell's unlike regions to the North. However, it is alive and well in test profiles and may just require additional load and/ or a change in slab properties before it reaches threshold and becomes reactive. The late-Jan crust/surface hoar layer (around 1m deep) and the mid-January surface hoar (around 1.5m deep) have been dormant for several weeks.
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.
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.