Regions
Kootenay Boundary.
The Special Avalanche Warning has been extended until January 4th. Stay vigilant and be cautious in your terrain selection. Touchy persistent slabs exist and human triggering is likely.
Confidence
Fair - Wind effect is extremely variable
Weather Forecast
Arctic air is dominant and the weather remains benign with cold and mostly clear skies through Wednesday. High level moisture is developing on Thursday bringing some cloud cover. Alpine temperatures will be steady near -15 accompanied by moderate NW winds. On Friday things begin to change, however; at this point confidence is poor with model solutions and precipitation amounts.
Avalanche Summary
We continue to get reports of skier-triggered, and remotely triggered slab avalanches up to size 2.5. These avalanches are failing on all aspects from 1900-2300 m on a buried surface hoar layer 30-70 cm below the surface. This layer remains touchy to light loads, like YOU.
Snowpack Summary
Up to 35 cm of light, low density snow overlies recently formed surface hoar. Strong northerly winds have transported the new snow onto southerly aspects creating stiff and reactive wind slabs. Up to 80 cm below the surface, a touchy weak layer of surface hoar sitting on a thick rain crust exists. This widespread weak persistent layer consisting of surface hoar/ facets and a hard rain crust was buried mid-December and continues to produce whumpfing and sudden planar characteristics in snowpack tests. It will likely remain sensitive to human triggering for the foreseeable future. Although high elevation slopes may not have the rain crust, they are still reported to have touchy buried surface hoar. 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.