Avalanche forecast

Kootenay Boundary

Apr 10 – 11, 2012Avalanche Canada
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Avalanche danger

Thu
Fri
Alpine
4 · High
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Sunny skies and freezing levels as high as 3500 m are continued Wednesday. As the snowpack deteriorates, natural avalanche activity is to be expected. Solar induced wet slabs may be large and run full path.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–7
    The March 26th layer should be on your radar through the forecast period. It's now down 100 cm, which could create a large avalanche if triggered. I'd be wary of triggering on steep unsupported slopes, especially on Southerly aspects.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely - Certain
    Size
    1–4
    Strong sun, and freezing levels up to 3200 m is forecast for Wednesday. Watch for loose wet avalanches, with potential for deeper slab avalanches on slopes that bake all day. Cornices are also weak, and could trigger slopes below.

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–6
    A cohesive slab up to 100 cm is sitting on the March 27th interface. With little freeze and skyrocketing freezing levels, wet slabs are likely to occur on this layer. Wet slabs may entrain more mass than expected, and run full path.

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

The weather pattern will begin to change tonight as a dominating ridge of high pressure will start to break down. This will allow a strengthening, moist SW flow to enter the region. Wednesday: Freezing levels will continue to be near 3000 m, with sunny skies and light SW winds. Thursday: Light precipitation should begin later Wednesday night, while Thursday may bring moderate-heavy amounts. Freezing levels will fall 1200-1500 m. Ridgetop winds light gusting moderate from the SW. Friday: Lingering, light precipitation through the day. Freezing levels may rise to 2000 m, with possible sunny skies in the afternoon.

Avalanche Summary

On Tuesday reports indicated widespread snowballing up to 2200 m with some natural loose wet avalanches up to size 1.5. On Monday a skier triggered slab avalanche (size 1.5) was reported. This occurred on a North aspect @1900, running 40 m wide and 80 m in length. Other observations from he field have indicated many loose wet slides from steep solar aspects up to size 2. I suspect loose wet, and wet slab avalanches to become a problem through Thursday. The danger ratings will remain elevated as we get hit by moderate-heavy precipitation on Thurs/Fri.

Snowpack Summary

Mild temperatures and spring-like conditions continue. A sun crust exists on solar aspects, while Northerly slopes host dry, wintery conditions down to 1400 m. Below the surface, the upper pack seems to be settling quickly with up to 100 cm of snow overlying the March 26th interface. This interface consists of a melt/freeze crust on all aspects except true north in the alpine, where small surface hoar (5mm) is present in sheltered places. This interface is a concern on true south aspects where the crust is thickest and where the surface hoar lurks. The snow at lower elevations has become moist and heavy during the warm sunny days. The persistent early February surface hoar lingers deep in the snowpack and may re-awaken with forecast skyrocketing freezing levels and mod-heavy precipitation on Thursday. Concern remains with heavy triggers (cornice), step down avalanches and rapid loading from intense precipitation, strong winds or sun.

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