Recently formed wind slabs may remain reactive to human triggers; especially where they are sitting on a slippery sun crust.
Large skier triggered persistent slab avalanches have surprised riders in the southern Selkirk mountains over the past week.
Recently formed wind slabs may remain reactive to human triggers in specific locations; especially where they are sitting on a slippery sun crust.
Cornices are very large in many areas, be aware of what's above your head.
Persistent weak layers of surface hoar and/or crust can be found 40 to 120 cm deep.
The problem is most likely found in the southern part of the Selkirks (e.g. Valhalla, Goat and Kokanee ranges), especially on open convex slopes at treeline elevations.
This problem exists on all aspects, however increased reactivity has been noted on northeast through southeast facing slopes.
Conservative terrain choices and disciplined decision making is required in areas where these persistent slabs remain active.
TUESDAY NIGHT: Clear / Light northeast winds / Low of -21 / Freezing level surface.
WEDNESDAY: Sunny / Light north wind / High of -9 / Freezing level surface.
THURSDAY: Mix of sun and cloud / Strong northwest wind / High of -6 / Freezing level valley bottom.
FRIDAY: Increasing cloudiness / Moderate northwest wind / High of -2 / Freezing level rising to 1200 m.
Several natural and skier triggered wind slabs were reported up to size 1.5 on Monday. They were primarily on northerly aspects.
Over the past week we have seen the buried weak layers of surface hoar and crust from mid February and late January produce very large persistent slab avalanches up to size 3. Activity has been concentrated in the Valhalla, Goat, and Kokanee Ranges typically on north through southeast facing slopes at treeline elevations.
The most likely triggers of these persistent slabs are strong solar radiation and/or large triggers such as smaller avalanches in motion, cornices, or snowmobiles.
Recent west and northwest winds have formed wind slabs on lee features at treeline and above. These slabs may remain more reactive on south facing slopes where they are sitting on a slippery sun crust. Below the recent snow, there may be a layer of small surface hoar that is likely most pronounced on northerly aspects or sheltered locations.
Lower elevations have seen warm temperatures last week and have a melt-freeze crust on the surface below 1800 m.
The late February persistent weak layer combination of crust, facets and surface hoar is buried up to 50cm deep, and has been reactive mostly on south facing slopes during periods of sun.
Two additional persistent weak layers sit 50-120 cm deep, from mid February and late January. They both consist of surface hoar and/or melt-freeze crusts. Recent trends indicate these layers have been more reactive in southern Selkirks around the Valhalla, Kokanee, and Goat Ranges. Several natural and human triggered avalanches have been produced on these layers in the last week. See the Avalanche Summary for full details.
The most likely triggers of these persistent weak layers are strong solar radiation and/or large triggers such as smaller avalanches in motion, cornices, or snowmobiles.
