Avalanche forecast

Northwest Inland

Mar 21 – 22, 2013Avalanche Canada
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Avalanche danger

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

The March 09 persistent weakness is very sensitive to human triggering and is producing frighteningly large avalanches.  Stay conservative in your approach to the mountains this weekend.

Avalanche problems

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2–6
    Large well developed cornices loom over many slopes.  Cornices may become more sensitive on slopes receiving direct sun.  It's likely that cornice failure will initiate large avalanches failing on the March 09 persistent weak layer.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–7
    A 30 - 60cm slab now rests on the March 09 surface hoar/crust combo.  This consolidated slab is very touchy and is subject to remote triggering from great distances. A very cautious approach to the mountains is appropriate at this time.

Confidence

Poor - Due to limited field observations

Weather Forecast

Synopsis: The pattern over the next five days starts out cool, convective and gusty. It will gradually turn milder, more stable and less windy towards SaturdayFriday: Freezing Level: Valley Bottom. Precip: No significant precip expected. Wind: Light, North.Saturday: Freezing Level: 600m Precip: No significant precip expected.  Wind: Light, NWSunday: Freezing Level: 600m  Precip: No significant precip expected. Wind: Light, South

Avalanche Summary

Wednesday's storm kicked off a natural cycle to size 3.  Skiers are remote triggering large destructive avalanches (size 2.5) from as far as 800m away. This adds to the numerous avalanches that are reported to have failed on this layer over the last few days.  I expect the trend to continue through the weekend.

Snowpack Summary

The region picked up 15 - 25 cm of new snow out Wednesdays storm which adds to the 20-40 cm snow that the region has received over the last few days.  This 35 - 65 cm of recent snow rests on a variety of old snow surfaces, including crusts, previous wind slabs and surface hoar (buried March 9th). Warmer temperatures and recent winds have now set this new snow into a reactive slab. The March 9th surface hoar layer is reported to be very touchy and appears to exist at all elevations and aspects.  It seams to be most electric on south through west facing slopes. I suspect cornices have become well-developed and could easily become unstable on slopes receiving direct sun. The mid snowpack is generally well settled and strong.

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