Kootenay Boundary

Fair - Timing, track, or intensity of incoming weather is uncertain

A polar warm front stalling north & west of the region will bring moderate to heavy precipitation to the surrounding areas Sunday. However, the Kootenay region will largely be "protected" from the action by a lingering ridge of high pressure. I expect scattered flurries in the region Sunday with snow amounts in the 1 - 3 cm range. Freezing levels rise to 1500m or so Sunday as the warm front affects the area. The trailing cold front associated with the system moves in late Sunday/early Monday bringing lower freezing levels and delivering 5 -10 cm of snow. Expect strong SW winds at & above treeline Sunday with a daytime high of 0 C @ 1500 m.

A skier-triggered avalanche near Nelson was reported from Thursday, running on wind slab over a crust. The avalanche was a size 2 and occurred on a north aspect, 40deg slope at 2125 m. The crown was 20-30 cm deep and the slide ran for 300-350 m. Recent activity on the mid-December surface hoar includes a snowcat remotely triggering a 70cm deep Size 2 slab avalanche from 10m away on a log-haul landing in a cutblock. Recent storm snow overlying a crust is also highly reactive to human triggers with slope-cuts producing numerous loose snow and 10-30cm thick slab avalanches up to Size 1.5. Continued whoomphing reported.

Recent new snow and gusty winds are keeping wind slabs and cornices fresh and weak, and in some places buried old wind slabs are a concern. A lightly buried thin crust extends into treeline elevations. Compression tests have been producing easy to moderate sudden results on the mid-December surface hoar, down 30-80cm, and propagation tests, whumpfing, and remote triggering suggest that avalanches associated with this persistent slab have a high propensity to propagate over large areas. Other weaknesses within the slab create the potential for step-down avalanches. Basal facets and depth hoar remain a concern in shallow rocky areas.