Regions
Kootenay Boundary.
Check out the Tricky Holiday Conditions blog post for more details on the current avalanche scenario.
Weather Forecast
A moist low pressure system will linger on Sunday bringing mostly patchy light snowfall, moderate northerly winds and freezing levels at valley bottom. By Monday a dry arctic ridge will set-up for the rest of the forecast period. With this ridge, we'll see mainly clear skies, light to moderate northeast winds and alpine temperatures around -20.
Avalanche Summary
On Thursday a party of skiers triggered a size 2 avalanche on a SW facing slope around 1800m in the Nelson area. Two people were reportedly caught and carried but thankfully ended up on the surface as everything came to a stop. In the north of the region on the same day, a size 2.5 natural slab avalanche failed at 2100m on a north aspect. The mid-December persistent weak layer was the likely failure plane in these events. This type of activity is likely to persist for the foreseeable future.
Snowpack Summary
Light to locally moderate amounts of low density snow have fallen and may have been shifted into wind slabs in high elevation terrain. This new snow overlies recently formed surface hoar.30 - 70 cm of snow from the last week is consolidating into a slab above a touchy weak layer formed in mid-December consisting of surface hoar sitting on a thick rain crust. This combo is thought to extend as high as 2400 m. This persistent layer will likely remain sensitive to human triggering for the foreseeable future. High elevation north facing slopes likely do not have the rain crust, but are still reported to have touchy buried surface hoar. On these slopes, deeper facets or buried surface hoar from earlier in the month may also be lurking. At the base of the snowpack, a crust/facet combo appears to have gone dormant for the time being.
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.