Regions
Banff Yoho Kootenay.
By definition the hazard is moderate treeline and below, however the potential still exists for human triggering of large avalanches in open terrain at these elevations. JH
Weather Forecast
Slight warming (highs of -7 by friday), increasing westerly wind(moderate on Wednesday) cloudy skies and light flurries are forecast through the rest of the week.
Snowpack Summary
Wind slabs in alpine and tree line areas. 30-60cm of snow over the Jan 6 surface hoar/facet/sun crust layer, which is becoming less reactive to skier triggering. Sudden collapse results persist on the Jan 6 and Dec 3 layers in the Kootenay region. Isolated whumphing on mid-pack facets/surface hoar today.
Avalanche Summary
Visitor Safety was able to trigger a size 1.5 wind slab on a SE steep alpine feature on Monday near Observation Peak. A large natural cornice collapse also occurred Monday in the Sunshine backcountry on Quartz Ridge. Lots of evidence of the previous widespread natural avalanche cycle up to size 3 on all aspects with some very large propagations.
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.