Avalanche Forecast
Kootenay Boundary
Watch for areas where the storm snow has settled into a cohesive soft slab above the recent crust/surface hoar layer. A prime combination for human triggered avalanches! Check out the Forecasters' Blog here for some great terrain advice.
Avalanche Problem 1: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Watch for signs of unstable snow or slab formation such as whumpfing, or shooting cracks.
- Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.
- Use conservative route selection, choose moderate angled and supported terrain with low consequence.
Avalanche Summary
On Friday storm storm was sloughing naturally in steep terrain with loose snow releases to Size 1, while skier traffic produced small slab releases to Size 1 in areas where the storm snow had formed into a slightly stiffer, cohesive slab above the December 15th layer.
On Thursday ski cutting produced small releases up to Size 1 failing within the storm snow. On Wednesday numerous Size 1-2 skier, remote, and explosives triggered slab avalanches on primarily north to west aspects between 1800-2100m, failing both within the storm snow and on the December 15th crust/surface hoar layer; including a Size 1.5 skier accidental.
Earlier in the week numerous natural and skier controlled storm slab avalanches to Size 2 were observed on a wide variety of aspects and elevations, while explosive control produced numerous storm slab avalanches to Size 2.5-3 on southeast to southwest aspects.
Also several classic signs of instability (whumpfing, shooting cracks, easy sudden results in snowpack tests) continue to be reported since Monday. See the Mountian Information Network (MIN) for great recent reports here, here and here, as well as a video here.
Snowpack Summary
Storm snow totals over the past week average between 50-90 cm across the region. This new snow has fallen on the "December 15th crust/surface hoar layer", a variety of old snow surfaces depending on aspect and elevation. On solar aspects a thin melt-freeze crust has been buried. On northerly aspects, feathery, surface hoar crystals (10-60 mm in length) have been buried below treeline as well as protected areas at treeline. In the alpine the old surface consisted of sugary snow (facets) and hard, wind scoured snow. Recent snowpack tests have produced very easy to hard, sudden and resistant results on the December 15th crust/surface hoar layer, indicating a high degree of variability and uncertainty in this layer. Below the December 15th layer, the late November crust is now buried 70-100 cm. Beneath this crust the lower snowpack is well settled.
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Weather Forecast
SUNDAY: Mostly sunny. Ridge wind light from the northwest. Temperature -12. Freezing level surface.
MONDAY: Mix of sun and cloud, flurries. Accumulation trace. Ridge wind light from the north. Temperature -12. Freezing level surface.
TUESDAY: Mix of sun and cloud. Ridge wind light from the northwest. Temperature -15. Freezing level surface.
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Recent storm snow has settled into cohesive soft slabs above the December 15th crust/surface hoar layer. Expect these slabs to be easily triggered especially on steep or convex slopes and sheltered areas where surface hoar has been buried.