Avalanche forecast

Northwest Inland

Mar 22 – 23, 2013Avalanche Canada
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Avalanche danger

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

The March 9th 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
    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.

  • Persistent 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 mountain travel is appropriate at this time.

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

Synopsis: Fine weather for the weekend. A weak system will bring flurries for Monday.Saturday and Sunday: Clear and sunny. Daytime alpine temperatuers around -5, but feeling warmer in the sun. Light winds.Monday: Cloudy with flurries. Afternoon freezing level rising to 1900 m. Southeast winds to 30 km/h.

Avalanche Summary

On Thursday, human-triggered avalanches were reported running on a the March 9th surface hoar layer on north and northwest aspects. Natural avalanches up to size 2 were also observed on lee slopes below steep ridge lines. On Wednesday, there was a natural cycle to size 3.  Skiers were remote triggering large destructive avalanches (size 2.5) from as far as 800m away. It has been an active recent period, with numerous avalanches reported to have failed on the March 9th layer over the past week. The trend is likely to continue through the weekend.

Snowpack Summary

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 set this new snow into a reactive slab. The March 9th surface hoar layer is reported to be very touchy. The surface hoar may not exist, or be reactive, in every drainage. Where it does exist, it appears to be present at all elevations, but is likely to pose the biggest threat in the alpine. Recent reports indicate it has been more reactive on south through west aspects, but I wouldn't necessarily trust steep north or east facing slopes at this time either.  I suspect cornices have become well-developed and could easily become unstable during periods of warm weather or on slopes receiving direct sun. The mid snowpack is generally well settled and strong.

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