Avalanche forecast

Kootenay Boundary

Apr 19 – 20, 2016Avalanche Canada
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Avalanche danger

Thu
Fri
Alpine
No rating
Treeline
No rating
Below
No rating
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Highlights

Spring Conditions. Record setting temperatures and ongoing sunny weather will increase the likelihood of large destructive wet slab avalanches, especially if there is little or no overnight refreeze of the snow surface.

Avalanche problems

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–4
      If the sun is shining, cornices present a significant hazard. Even if they don't trigger a slab avalanche when they fall onto a slope, they have a nasty habit of running surprisingly long distances.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–3
    Solar radiation in the spring can rapidly change the hazard from low to high. Plan ahead and monitor the effect of solar radiation carefully.

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    3–6
    Extremely high freezing levels and little to no overnight surface freeze will increase the potential for sporadic deep wet slab release.

Weather Forecast

WEDNESDAY: Freezing Level: 3700m, sunny, light southerly ridgetop winds. THURSDAY: Freezing Level: 3500m, sunny in the morning, then increasing cloud in the late afternoon, light southerly ridgetop winds. FRIDAY: Freezing Level: 3300m, mix of sun and cloud, light southerly ridgetop winds.

Avalanche Summary

Most commercial operations have closed for the season, and data is becoming sparse. However, with the extremely high freezing levels, sunny skies, and lack of overnight surface freezing, I would expect cornice failures and sporadic large wet slab avalanches.

Snowpack Summary

Monitoring the overnight freeze of the snow surface is very important during the spring. If the snow surface does not freeze overnight or if the crust is only a few cm thick, the effect of daytime heating and solar radiation will weaken the snowpack much more quickly than it would if there is a well frozen thick crust. This is because the crust must first melt before the sun can weaken the snowpack. Deeply buried weak layers in the mid snowpack and near the ground still have the potential to wake up and become active with a rapid warm up. While unlikely, releases on these deeply buried weak layers would result in very large avalanches. Glide cracks are widespread, active, and best avoided. Cornices are large, fragile, and could trigger deep slab avalanches that run to valley bottoms. The snowpack in many areas has become isothermal, meaning the snowpack is 0 degrees Celsius throughout. An isothermal snowpack is more prone to full depth wet slab avalanches during the heat of the day.

Regions covered