Regions
Kootenay Boundary.
It's getting trickier, new snow and wind Friday night will likely form sensitive storm slabs and could push the persistent slab problem to natural failure. With all this uncertainty its best to stay conservative with terrain selection this weekend.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
One last blast of Pacific moisture is set to clash with the Arctic air mass over the province as a low pressure system moves towards the Lower Mainland late Friday. This storm is expected to deliver significant snow and wind all of Friday night, exiting to the east Saturday morning. Look for cold dry weather on Sunday and Monday.FRIDAY NIGHT: Freezing level at valley bottom, 5 to 25 cm of snow possible, moderate to strong southwest wind through the night.SATURDAY: Skies clearing throughout the day, freezing level at valley bottom, moderate to strong northwest wind, 1 to 10 cm of snow possible.SUNDAY: Clear skies, freezing level at valley bottom, light variable wind, no snow expected.MONDAY: Clear skies, freezing level at valley bottom, light variable wind, no snow expected.
Avalanche Summary
On Thursday control work produced storm slabs on southeast through southwest facing slopes up to size 2.5. Loose dry avalanches to size 2.5 were also reported. On Tuesday a skier triggered a size 1.5 wind slab on a north-facing alpine slope in Kokanee Glacier Provincial Park. The skier went for a short ride, but was uninjured in the event.
Snowpack Summary
Thursday's storm produced 10 to 25 cm of low density snow which was accompanied by light to moderate wind out of south, southwest and even a bit of of southeast. The new snow overlies recently buried surface hoar, although at this point not much is known about the size or distribution of this potential weak layer.Between 25 and 80 cm below the surface you'll find the December 15th interface which consists of a melt-freeze crust on steep, solar, higher elevation slopes and well-developed surface hoar which seems most pronounced in sheltered terrain at and below treeline. The bond at this variable interface is of critical importance, especially in areas where the overlying slab is deep and well-consolidated.The late November crust is now buried 60 to 100 cm below the surface and has been producing hard, resistant results in recent snowpack tests. Beneath this crust the lower snowpack is strong and well-settled.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.
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.