Regions
Banff Yoho Kootenay.
An upslope storm is crossing the region tonight bringing more snow to southern areas and strong east winds. Be wary as additional load develops over the Dec 15 persistent weak layer.
Weather Forecast
Northeast flow affects the regions tonight with another 10-15 expected, mostly in the southern part of the forecast region (SSV). Less snow north (Bow Summit). N and E winds up to 70 km/hr expected overnight, with temperatures remaining cool at -12 to -15. Storm ends Wednesday morning with scattered flurries through Thursday. Sunshine for Xmas...
Snowpack Summary
10-30 cm of soft snow now covers the Dec 15 persistent weak layer of surface hoar, sun crust or facets (depending on location). An additional 5-10 cm and strong NE winds are expected overnight Tuesday and may create windslabs in unusual locations (reverse loading). These will be very sensitive to triggering soft slab avalanches.
Avalanche Summary
Widespread small soft slab avalanches were observed on Monday, and to a lesser extent on Tuesday at the local ski areas. Generally these have been size 1 avalanches with little mass, but we expect their size to grow with the additional snow. Loose snow avalanches have also been observed in steep gullies.
Confidence
Forecast snowfall amounts are uncertain on Wednesday
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.
Loose Dry
Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.