Regions
Banff Yoho Kootenay.
Enjoy the new snow, but remember that there is enough whumphing and avalanche activity on the mid-pack weak layers to continue with a cautious approach to larger more committing terrain.
Weather Forecast
We should see some new snow Sunday night and into Monday with models showing between 5-10 cm of snow at treeline. Temperatures will remain below freezing with -10 to -12'C at upper elevations. 3000m winds will be moderate/strong SW Sunday night then dropping Monday. Tuesday sees a slight clearing trend and perhaps some more flurries on Wednesday.
Snowpack Summary
Newly formed wind slabs in immediate lee features at alpine and treeline elevations. In sheltered areas the upper snowpack consists of 20-30cm of soft slab over the Jan 6 surface hoar. The Dec 15 layer of surface hoar and facets is down 40-60 cm and is reactive in snow tests. Below treeline much of the snowpack is facetted with little structure.
Avalanche Summary
Two size 2 slabs triggered by wind loading and cornice failures were observed in the last 24 hours on Quartz Ridge and the 93 North. These both appeared to fail on a mid pack layer of facets. One skier triggered size 1 wind slab was reported in Semi Circular Bowl near Lake Louise. Numerous large sluffs out of steep rocky terrain in the last 36 hrs.
Confidence
Intensity of incoming weather systems is uncertain on Monday
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.