Avalanche forecast

Kootenay Boundary

Feb 19 – 20, 2016Avalanche Canada
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Avalanche danger

Sun
Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

If winds are strong and new snowfall amounts exceed 20cm in your area, Saturday`s Avalanche Danger may be HIGH in alpine.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–3
    Storm loading on Friday night will create fresh and reactive wind slabs in exposed lee terrain. New snow may also react as a loose dry avalanche in steep sheltered terrain.

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–4
    Recent stormy weather has encouraged cornice growth. Large and fragile cornices may be destructive by themselves, but they may also act as a trigger for a large avalanche on the slope below.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–5
    A buried crust and surface hoar layer lie up to 100cm below the surface. Although you may not see this weakness on every slope, avalanches at this interface may be surprisingly large. I would maintain respect for this layer for the foreseeable future

Confidence

Moderate - Forecast snowfall amounts are uncertain on Friday

Weather Forecast

A brief pulse will bring 15-25cm of new snow to the region on Friday night. Expect gradual clearing throughout the day on Saturday and mainly clear skies on Sunday. On Sunday night the region may see up to 5cm of new snow, but more clearing expected on Monday. Ridgetop winds will be generally moderate from the southwest with Friday and Sunday nights` systems; otherwise, they will remain mainly light. Freezing levels should hover between 1300 and 1500m for the forecast period.

Avalanche Summary

On Thursday, numerous naturally triggered storm slab avalanches were observed in the size 1.5-2 range. They failed in response to heavy storm loading on Wednesday night and Thursday. Throughout the week, a few skier triggered size 1.5-2 avalanches were also reported. A few of these avalanches failed on the February crust interface mentioned in the Snowpack Discussion section. Of note, a size 2 slab avalanche northwest of Kaslo (in the South Columbia region) partially buried 2 people and completely buried another person. The avalanche, which failed on the early February crust interface, occurred on an east aspect at 1700m. Nobody was injured in the avalanche, but it points to the touchy conditions which also extend south into some parts of the Kootenay Boundary region. New snow and wind on Friday night will deliver its own mix of wind slab activity, but storm loading will also add to the likelihood and consequences of avalanches failing on the buried early February crust.

Snowpack Summary

On Friday night, 15-20cm of new snow is expected to fall and overlie settling storm snow from the past few days. Moderate southwest winds are forecast to shift these accumulations into deeper and more reactive wind slabs in exposed lee terrain. 60-100 cm below the surface you'll find a hard melt-freeze crust which formed during the 2nd week of February. This crust is quite widespread and may co-exist with weak surface hoar or facets. This variably reactive interface is the critical layer to watch in the region as it has caught a few people by surprise in recent days. A few buried surface hoar layers exist in the top 100 cm in drier areas on the west side of the region near Rossland. In other areas the notable early January surface hoar layer is 100-170 cm deep and poses a low probability/ high consequence threat. It should remain on your radar, especially in thin snowpack areas and during periods of significant warming or rapid loading.

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