Regions
Banff Yoho Kootenay.
We have reached the tipping point for avalanches. Natural activity has slowed down, but the snowpack is perfectly primed for human triggering. Step way back in terms of your terrain use and exposure.
Weather Forecast
Temps. will be in the -5 to-10C range for Saturday, and slightly cooler in the alpine. At treeline we could see 10-15cm in Kootenay, 5-10 in Lake Louise, and 3-5cm in the Banff by the end of the day, with light to mod. S - SW upper level winds (3000m). An "atmospheric river" may enter our region Sunday night which could cause an avalanche cycle.
Snowpack Summary
55-75cm of snow has fallen over the past 10 days creating a lot of loose snow on the surface. Alpine winds have distributed this into leeward areas with wind slabs up to 1m thick. Three persistent weak layers lurk in the upper half of the snowpack: Jan 16 down 20-40cm; Jan 6 down 30-50cm; Dec15 down 40-80cm giving easy-mod test results.
Avalanche Summary
There was a fairly widespread avalanche cycle yesterday to size 3 with wind slabs and persistent slabs failing. Less activity Friday but still some sporadic size 2-3 persistent slabs failing in the region.
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.