Regions
Banff Yoho Kootenay.
There's plenty of loose snow available for transport, and big winds are forecast for Friday and Saturday. This in conjunction with incoming snow will likely induce another avalanche cycle.
Weather Forecast
Fridays big story will be the forecasted alpine winds in the 70 - 100kmh range and rising temperatures in front of the next system. Banff is forecast only for a couple cm, and Lake Louise in the 10cm range. By Saturday night Banff could see 10cm and regions near the divide could see 20+ cm. We expect another avalanche cycle given this forecast.
Snowpack Summary
40-80 cm of snow over the last seven days has overloaded 3 persistent weak layers of surface hoar and facets in the upper half of the snowpack: Jan 16 down 30-50cm; Jan 6 down 40-70cm; and Dec15 down 50-100+cm. A major avalanche cycle occurred Monday/Tuesday with avalanches running fall path on these layers and some stepping down even deeper.
Avalanche Summary
Natural activity has tapered slightly, but big results with explosives over the last few days to size 3.5 proves that these layers are prime for triggering. Some avalanches ran full path and put dust or debris on roads. Many slopes haven't slid yet, and any additional input (snow/wind/human) will overload the snowpack.
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.
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.