Regions
Kootenay Boundary.
Jump over to avalanche.ca/blogs to learn more about the persistent slab problem.
Confidence
Fair - Due to the number of field observations
Weather Forecast
Synopsis: Light precipitation is possible Saturday afternoon as a weak system passes over the SE portion of the province. On Sunday a strengthening ridge of high pressure drives cold and dry conditions that will likely persist for the next week. Saturday: Freezing Level: Valley Bottom; Precipitation: 2-5mm | 2-10cm; Wind: Treeline: Light, SW | Ridgetop: Strong, W.Sunday: Freezing Level: Valley Bottom; Precipitation: Trace; Wind: Treeline: Light, E/NE | Ridgetop: Moderate to Strong E/SE.Monday: Freezing Level: Valley Bottom; Precipitation: Nil; Treeline: Moderate, NE | Ridgetop: Moderate, NE.
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. This type of activity is likely to persist for the foreseeable future.
Snowpack Summary
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 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.