Avalanche forecast

South Columbia

Mar 20 – 21, 2016Avalanche Canada
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Avalanche danger

Tue
Wed
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Watch for fresh storm slab formation at upper elevations and continue to seek out conservative terrain in an effort to avoid tangling with the late February persistent weak layer.

Avalanche problems

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    3–5
    Large unstable cornices overhang countless ridge lines and many of these cornices are teetering on the brink of failure.  The weight of an approaching rider, a bit of wind or a period of sunshine could easily induce natural collapse.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3–6
    The late February weak layer is becoming less sensitive to triggers, but it has not gone away and it continues to produce very large natural avalanches.  Continue to seek out conservative terrain as you plan your day in the mountains.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–2
    Sunday night's storm should produce 5 to 10 cm of new snow accompanied by moderate to strong southwest winds.  Watch for fresh slab formation in wind exposed features at and above treeline.

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain on Sunday

Weather Forecast

A weak upper low moves into the region Monday displacing the ridge that was in place over the weekend.  With the ridge collapsed, the door is open to a series of fast moving storms interspersed by the odd ridge.  SUNDAY NIGHT: Freezing level around 1900 m, 5 to 10 cm of snow above 1900 m, rain below, moderate southwest wind.  MONDAY:  Freezing level around 1700 m, 1 to 8 cm of snow at and above treeline, light to moderate southwest wind. TUESDAY: Freezing level starting near valley bottom rising to about 1700 m, light variable wind, no significant precipitation.  WEDNESDAY: Freezing level starting near valley bottom rising to about 1500 m, 1 to 5 cm of snow possible, light southwest wind.

Avalanche Summary

On Saturday cornice fall produced avalanches to size 3 on north and northeast facing features between 2000 and 2400 m, failing on the late February persistent weak layer.  Small natural storm and wind slabs were also reported on northwest, northeast and east facing slopes between 2100 and 2400 m. 

Snowpack Summary

Large cornices loom over many ridge lines and many are teetering on the brink of failure. Old wind slabs may remain a problem on high elevation north facing features. The make up of the late February persistent weak layer is an aspect dependant mix of surface hoar, facets and/or a thick crust down around 60 to 110 cm below the snow surface. Large triggers like natural cornice fall and explosive control work continue to initiate avalanches failing on this interface. The recent warm to cool temperatures should give the overlying slab a bit of strength, but it has yet to prove itself trustworthy. Unfortunately there's not much of a reliable pattern telling us what exact aspects are most suspect. As a precautionary measure, we recommend remaining suspicious of steep unsupported features at and above treeline.

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