Regions
Kootenay Boundary.
Weather Forecast
Wednesday: Continued light snowfall picking up in the evening, with moderate to strong southwesterly winds, and freezing levels as high as 2000m in the morning before dropping to 1000m late in the day. Thursday: 5-15cm possible by the morning, then light snowfall throughout the day with freezing levels in valley bottoms and light, but gusty, westerly winds. Friday: Generally dry with isolated flurries possible.
Avalanche Summary
There are two new reports of skiers remotely triggering avalanches running on the mid-December surface hoar. One was relatively small on a steep lee slope triggered from a ridge 10m away. The other was a 30-80cm thick Size 2 that was triggered by a cornice fall, which was remotely triggered from a skier 3m away on the ridge crest.
Snowpack Summary
New snow and gusty winds are keeping wind slabs and cornices fresh and weak, and in some places buried old wind slabs are a concern. Compression tests have been producing easy to moderate sudden results on the mid-December surface hoar, down 30-80cm, and propagation tests have shown that avalanches associated with this persistent slab have a high propensity to propagate over large areas. Continued warm temperatures will likely make persistent slabs particularly touchy on Wednesday, before colder temperatures start to lock things up later in the forecast period. Basal facets and depth hoar remain a concern in shallow rocky areas.
Problems
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.
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.