Regions
Kootenay Boundary.
Recent snowpack and avalanche observations from the Rossland Range indicate that the Danger Rating below treeline is CONSIDERABLE. The Special Public Avalanche Warning is extended through the weekend.
Confidence
Fair - Intensity of incoming weather systems is uncertain
Weather Forecast
Increasing cloud, moderate west winds and some light flurries are expected overnight Thursday. On Friday, cloudy skies with snow amounts near 5 cm. Alpine temperatures near -10. A brief lull in the pattern for Saturday as a second Pacific low deepens off the coast. This low could bring moderate amounts of snow to the Interior Sunday afternoon and overnight into Monday, however; confidence is poor with timing and precipitation amounts due to model discrepancies.
Avalanche Summary
In the Rossland Range, reports indicate that the mid-December crust/ surface hoar/ facet layer seems to be very touchy and numerous naturals and human triggered avalanche activity has occurred over the past few days. Elevations ranging from 1900-2300 m seem to be hot spots, and conservative terrain selection is critical even in the trees where you tend to let your guard down. Reports from other parts of the region indicate a skier remote size 2 (15 m away) on a west aspect at 2100 m and a skier triggered size 1 on a west aspect at 2170 m, both of these failing on the mid-December surface hoar. In locations that have seen more wind, this layer sensitivity is touchy to light loads, like YOU.
Snowpack Summary
Snow surfaces are variable with northerly, wind exposed aspects showing firm wind press or scoured exposed crust, and sheltered locations have up to 35 cm of light, low density, faceted snow above a 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 persistent weak layer comprising 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. 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.