Regions
Banff Yoho Kootenay.
Two days of avalanche control has produced mixed results. Most areas in Banff, Yoho and Kootenay produced only a few avalanches to size 2. However, down in Little Yoho we triggered several large size 3s that blew over the climbs and covered the road.
Weather Forecast
The ridge of high pressure is breaking down and a Pacific storm will cross the region starting Wednesday afternoon. Wednesday itself will be colder (-4 to -10) with winds picking up from the west and snow starting in the afternoon. Expect up to 15 cm by the end of the storm on Thursday afternoon.
Snowpack Summary
Recent warm temperatures aloft have settled the upper snowpack and formed suncrust on S and W aspects. 30-50cm of snow sits over the Dec.15 persistent weak layer of facets and surface hoar. The overlying slab propagation is extremely variable across the region with stability of the snow being specific to each slope.
Avalanche Summary
Two days of avalanche control has produced smaller results than expected in all areas except near Field. Bourgeau, Whymper, Simpson and Bosworth each produced a few avalanches up to size 2 failing on the Dec 15 facet layers, but the results were not as widespread as anticipated. Mt. Dennis ice climbs in Field produced large avalanches up to size 3.
Problems
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.