Avalanche forecast

Purcells

Mar 15 – 16, 2013Avalanche Canada
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Avalanche danger

Sun
Mon
Alpine
4 · High
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Freezing levels are uncertain, making forecasting for Saturday challenging. If you're traveling on a thickly refrozen surface, chances are avalanche danger's not too bad.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2–7
    A weak interface buried over a metre deep could still be triggered with a heavy load, like cornice fall, or from a thin-spot trigger point.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–6
    Recent storm snow will take some time to stabilize. It may be most reactive where the wind has shifted it into slabs on lee slopes.

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    1–6
    If temperatures remain warm at low elevations, the rain-soaked snowpack has the potential to fail at ground. If it refreezes overnight, this problem should sort itself out.

Confidence

Fair - Freezing levels are uncertain on Saturday

Weather Forecast

Saturday: Light snow, starting late in the day. Moderate to strong W winds. Alpine temperature near -6.Sunday: Light to moderate snow. Moderate to strong NW winds. Alpine temperature near -7.Monday: Light snow. Light SW winds. Alpine temperature near -12.

Avalanche Summary

A widespread natural avalanche cycle was observed over the last two days,  including loose dry and soft slab avalanches at the beginning of the storm, and wet avalanches as it warmed up. Skiers also triggered wind slabs on lee slopes. Most avalanches were in the size 1-2 range (with a few at size 3) and failed within, or at the base of, the storm snow.

Snowpack Summary

The recent storm dropped anywhere from 40 cm to 1 m of snow at upper elevations, while rain soaked the snowpack below treeline. The freezing level was between 1700 m and 2400 m during the storm. Strong NW through SW winds have redistributed snow into wind slabs and created cornices at alpine elevations. Below the storm snow is a layer of buried surface hoar and/or a crust, which is increasing the reactivity of storm slabs. Deeper in the snowpack, a weak interface buried in mid-February is still on the radar. Although unlikely to be triggered, it remains possible with a very heavy load or from a thin-spot trigger point. A facet/crust layer sits at the base of the snowpack in some areas.As temperatures cool, wet slab/loose wet avalanche problems should improve, but persistent slab concerns at upper elevations will linger, especially on slopes which didn’t avalanche during the storm.

Regions covered