Two important headlines: 1) the surface hoar problem has become very significant in Kootenay and probably in Yoho too. Avoid steep terrain at and below treeline, and 2) a big storm is coming, and an avalanche cycle will occur on Thursday and Friday. Avoid all avalanche terrain on these days.
SW winds have increased into the moderate-to-strong range with extreme gusts, building wind slabs in lee terrain. These winds have redistributed up to 30 cm of recent snow over the past week, creating reactive wind slabs at treeline and above.
A 30-40 cm slab over the Jan. 24th surface hoar layer is very touchy and will almost certainly release if you ski through any steep slope between 1600 and 2200 m in this area. The reactivity of this layer has increased significantly this week as the slab has stiffened.
No reports yet, but we expect windslab action up to size 2 in alpine areas.
At lower elevations, we continue to receive reports of increased reactivity of the surface hoar problem. This is very significant and getting worse. On Tuesday, our field team observed a size 2 avalanche in the Simpson area that ran 300 m through thick forest. Over the past week, there have been several skier-triggered avalanches on this problem to size 1.5.
Windslab development has been widespread since Monday, and these are reactive to human triggering. The Jan 24 layer (surface hoar/crust) is down 30-40 cm at treeline and has been super touchy in Yoho and Kootenay. Starting Wednesday afternoon, the snowpack's stability will deteriorate rapidly as the storm arrives and an avalanche cycle begins.
The weather begins to change on Wednesday as a strong westerly flow establishes itself, and by Thursday, we expect a significant storm to be upon us. This setup is the classic westerly flow collision with cold arctic air to the east. Some forecasts are calling for 35-40 cm of snow by Friday, along with winds exceeding 80 km/h. If this unfolds, we can certainly expect to see an avalanche cycle.
