Avalanche forecast

Kootenay Boundary

Apr 13 – 14, 2012Avalanche Canada
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Avalanche danger

Sun
Mon
Alpine
2 · Moderate
Treeline
3 · Considerable
Below
3 · Considerable
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Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    3–6
    A crust that developed in late March is now buried down close to a metre. Strong solar radiation and daytime warming may cause avalanches to step down and propagate on this layer causing large destructive avalanches.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–5
    Loose wet avalanches are expected during periods of daytime warming and during periods of rain showers. Overnight freezing above about 1200 metres should develop a hard crust that may deteriorate during the heat of the day.

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3–7
    Wet slab avalanches are expected during periods of daytime warming and during periods of rain showers. Overnight freezing above about 1200 metres should develop a hard crust that may deteriorate during the heat of the day.

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Saturday

Weather Forecast

A ridge of high pressure is expected to slowly move into the interior ranges on Saturday. Unsettled conditions with showers in the valleys and flurries above 1700 metres should continue during the day. Clearing skies are forecast by Saturday evening, which should bring the freezing level down to about 1200 metres overnight. Sunday should be mostly sunny with light variable winds and a chance of afternoon cloud building as the freezing level rises to about 1800 metres. The wind is expected to start to build out of the southwest on Monday as a low pressure system moves onto the south coast. It is a little too early to forecast when this system will push into the eastern ranges of the interior mountains.

Avalanche Summary

On Thursday, explosive avalanche control produced numerous avalanches on SE-SW slopes up to 2200 m. Loose wet, and wet slabs ran to size 3. The snowpack has been reported to be isothermic below about 1500 metres and likely to be scrubbed down to the ground if releases from above make it down to lower elevations. Forecast high pressure may bring back more of a melt-freeze cycle above 1200 metres. Moist and wet avalanches are expected to continue during daytime warming or periods of rain showers.

Snowpack Summary

Spring-like weather has transformed the snowpack significantly in the last 5 days. Melt-freeze conditions have existed, promoting crusts on solar aspects at all elevations. Melt-freeze crusts also exist on all aspects up to 1500 m. Below treeline elevations have seen more of the melt than the freeze, and the upper snowpack has become quite moist. Northerly aspects at upper elevations still host dry, wintery snow. With forecast snow, small wind slabs may be building at higher elevations. These may be found hiding behind terrain features, or in the immediate lee of ridgecrests. 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 mid February surface hoar layer is buried deep in the pack; this is a low probability high consequence scenario and may take a significant event to be triggered from a specific location. Concern remains with heavy triggers (cornice), step down avalanches and rapid loading from intense precipitation, strong winds or sun.

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