Regions
Kootenay Boundary.
Reports of whumpfing and remote triggering indicate a weak layer buried at the beginning of January may still be sensitive to light loads. Choose conservative terrain and watch for clues of instability.
Confidence
Moderate - Wind speed and direction is uncertain on Tuesday
Weather Forecast
On Tuesday night up to 15cm of new snow may be expected with light to moderate ridgetop winds. By the afternoon, we should expect a mix of sun and cloud and light northwest winds. On Thursday and Friday a series of Pacific systems will move through the region bringing up to 15cm of new snow and strong southwest winds each day. Freezing levels should sit at valley bottom on Wednesday and then rise to about 1300m on Thursday and Friday.
Avalanche Summary
In the north of the region on Monday, a few persistent slab avalanches to size 2 were remotely triggered between 1600 and 1700m from a distances of about 5 metres. This demonstrates the sensitive nature of this instability in some areas. A skier also ski cut a size 1 persistent slab avalanche in the Kootenay Pass area. The early January surface hoar was the culprit in all of these events. New snow and wind on Tuesday night may also spark a new round of wind slab activity on Wednesday.
Snowpack Summary
Up to 15cm of new snow is expected on Tuesday night. If ridgetop winds are in the moderate to strong range, new wind slabs can be expected in upper elevation lee terrain. 40-60 cm below the surface you'll find a weak layer of surface hoar and a hard crust on steep solar aspects. This layer seems variably reactive. Some test results suggest an improving bond at this interface while remote triggering and Mountain Information Network reports of whumpfing show this layer is still sensitive to light loads in some areas. I would be increasingly cautious in areas where the overlying slab is deep and has gained cohesion through wind pressing, warming, and/or settlement. The mid and lower snowpack are generally well settled and strong.
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.