Regions
Banff Yoho Kootenay.
Heads up! Climbers and skiers should manage their overhead exposure carefully and choose conservative terrain as large avalanches are likely at all elevations. Widespread touchy slabs are ripe for human triggering.
Weather Forecast
Light flurries can be expected Sunday in western regions of the forecast area with a mix of sun and cloud in other areas. Alpine temperatures will range from -10 to -15 with light winds out of the NW. A clearing trend is expected on Monday as alpine temperatures cool to -16 to -18 with continued light NW winds.
Snowpack Summary
Touchy wind slabs in alpine and treeline areas, and fragile new cornices in the alpine. 30-50 cm of snow sits over the Jan 6 surface hoar/facet layer and is reactive to skier triggering. We have experienced many large whumphs over the last several days with failures on both the Jan 6 surface hoar/facets, and in the mid pack facets below this layer.
Avalanche Summary
Several natural avalanches were observed Saturday up to size 2. This follows an extensive natural cycle of avalanches up to size 3 during the past 48 hours with slabs propagating up to several hundred meters and over 40cm deep on many slopes. Conditions remain ripe for human triggering and occasional large natural avalanches.
Confidence
Due to the number and quality of field observations
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.