Avalanche forecast

Purcells

Dec 11 – 12, 2013Avalanche Canada
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Avalanche danger

Fri
Sat
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

If you receive more then 15 cm of new snow in your local riding area, consider the danger ratings to be one step HIGHER.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–3
    Shifting winds have redistributed snow forming wind slabs in lee terrain. Wind slabs found especially on southwesterly aspects are not typical, and they may surprise you.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    2–5
    In deeper snowpack areas, it may be possible to trigger an avalanche on a layer of buried surface hoar. In shallower ones, watch for a weak sugary facet layer near the base. The most likely place to trigger them is on steep, convex slopes.

Weather Forecast

Interior regions will start to see light-moderate amounts of snow, gradual warming and strong ridgetop winds as the weakening cold front passes through on Thursday. The Northern part of the Purcells may see fewer accumulations.Thursday: Cloudy. Snow amounts 10-15 cm. Alpine temperatures near -9. Ridgetop winds moderate from the West.Friday: Precipitation will taper off as we see a break in the system. Cloudy skies, snow amounts near 5 cm. Alpine temperatures -9. Ridgetop winds strong from the West.Saturday: Cloudy with snow amounts near 5 cm. Alpine temperatures -7. Ridgetop winds moderate from the SW.

Avalanche Summary

Wind slab avalanches up to size 1.5 have been easily triggered under the weight of a rider, most commonly on N-NE aspects, cross-loaded features and the immediate leeward side of ridge crests. Loose dry surface sluffing from steeper terrain is expected, use caution near terrain traps like cliffs, and depressions.

Confidence

Fair - Timing, track, or intensity of incoming weather system is uncertain

Snowpack Summary

Shifting winds have formed stiff wind slabs on the lee side of ridge lines. Snowpack depths at treeline vary across the region, averaging 70-110 cm. Widespread surface hoar development and surface faceting exists from the previous cold temperatures and is now getting buried by incremental snowfall amounts. In the Southern part of the region there is 40-70cm of low density snow over the late-November surface hoar/ crust/ facet interface. This layer may become reactive as it sees additional load, and warming temperatures, forming more of a slab.In the Northern part of the region the lower/mid snowpack is weak, composed of an early season crust (more prevalent on north aspects) weak faceted crystals and depth hoar above and below the crust. This persistent slab may be stubborn to trigger, but if triggered have high consequences.

Regions covered