Regions
Banff Yoho Kootenay.
Climbers and skiers should all manage their overhead exposure and choose very conservative terrain at all elevations as large avalanches are likely. Widespread touchy slabs are ripe for human triggering.
Weather Forecast
Following a some clear skies on Friday we expect more unsettled conditions through the weekend. Flurries can be expected Saturday with alpine temperatures from -10 to -14 and light to moderate West winds. Mainly cloudy skies for Sunday with alpine temperatures cooling to -16 overnight and winds shifting to the NW and backing to light.
Snowpack Summary
Thursday's storm added 10 to 25cm with strong SW winds and freezing levels to approx. 1900m. Widespread unstable slabs exist with 30 to 100cm sitting on weak faceted crystals and surface hoar. Wet conditions BTL yesterday refroze overnight and crusts will now help hold things together where they are of sufficient thickness (below about 1900m).
Avalanche Summary
With today's clearing an extensive cycle of natural avalanches to size 3 were observed mainly above 1900m centered along highway 93N. Slabs propagated several hundred meters wide and over 40cm deep on many of the open slopes.While less activity has been seen in other parts of the region, conditions are ripe for human triggering and large avalanches
Problems
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.
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.