Avalanche forecast

South Columbia

Mar 20 – 21, 2013Avalanche Canada
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Avalanche danger

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

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–6
    The March 10th weak layer of surface hoar is buried down more than a metre in most places. Large loads like cornice falls may trigger this deeply buried weak layer.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1–4
    New storm slabs continue to develop due to strong winds and new snow. Deep pockets of wind transported snow continue to develop and may release naturally or with light additional loads. New cornice growth may be extensive and weak.

Confidence

Fair - Forecast snowfall amounts are uncertain on Thursday

Weather Forecast

Overnight and Thursday: Winds becoming Westerly moderate to strong overnight as the snow continues to fall across the region. Expect another 5-15 cms overnight and another 5-10 cms during the day. Alpine temperatures should drop down to near -10.0, and the freezing level should be at valley bottoms.Friday: Unsettled weather with mostly cloudy skies and strong to very strong gusty Northwest winds. Continued cool temperatures in the alpine and freezing levels rising to about 1000 metres during the day.Saturday: A ridge of High pressure is moving into the region bringing light West winds, clearing skies, and alpine temperatures in the -10.0 - -15.0 range.

Avalanche Summary

Natural cornice falls were reported from both the Selkirks and the Monashees up to size 2.5. Some solar triggered avalanches up to size 2.5 on steep South aspects. Pockets of wind slab were controlled by skiers up to size 1.5 on Tuesday. I suspect that wind slabs and storm slabs were more frequent on Wednesday after the strong winds and new snow.

Snowpack Summary

There is quite a bit of variability with respect to the amounts of new snow over the last few days. Some upslope areas had 30-40 cms of storm snow, and then another 20-30 cms on Wednesday. The recent storm amounts are between 20-60 cms at higher elevations. Strong winds overnight and early Wednesday morning developed thick pockets of wind slab at higher elevations. Cooling temperatures have promoted bonding to the moist snowpack at lower elevations. New cornice growth is reported to be extensive and weak. Expect natural cornice falls that may trigger weak layers that are buried down a metre or more on slopes below. The new storm load may trigger the March 10th weak surface hoar layer.

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