Avalanche forecast

Northwest Coastal

Mar 12, 2019Avalanche Canada
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Archived · expired 8 years ago

Avalanche danger

Wed
Thu
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

The snowpack needs time to adjust to the shock of a big, long awaited storm. With surface hoar and sugary facets below the new snow it may take longer than usual to stabilize.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3
    Higher new snow amounts are making old surface hoar and sugary facets in the upper snowpack layers to watch.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–3
    Previous weaknesses in the upper snowpack (30 - 40 cm of sugary facets) may become activated resulting in larger avalanches than expected. See Persistent Slabs below.

Confidence

High -

Weather Forecast

MONDAY NIGHT: Clearing off and drying out with only flurries. Light to moderate west wind.TUESDAY: Cloudy with sunny periods. Treeline temperatures -5 to -10 C. Light southwest winds.WEDNESDAY: Mix of sun and cloud. Dry. Treeline temperatures around -8 C. Light south wind.THURSDAY:  5 to 10 cm new snow. Moderate south wind. Treeline temperatues -5 to -10 C.

Avalanche Summary

Initial reports from the field today (Monday) suggest whumpfing, cracking, remotely triggered avalanches, and a widespread avalanche cycle on Monday morning.

Snowpack Summary

Widespread and reactive storm slabs and wind slabs. The 40 to 60 cm of storm snow covers a wide variety of surfaces but the key idea is they're all crappy. Avalanche forecasting rule of thumb:  the longer snow is exposed on the surface the less likely it is to bond when covered. We've just covered surface hoar, sun crusts, and a widespread weak faceted (sugary) upper snowpack. Early reports suggest the old surfaces, as old as the Feb 19 surface hoar facets is the critical weak interface so avalanches are running deeper / bigger than might be expected. The upper- and mid-pack weakened with the extended cold drought so there are widespread areas with soft faceted snow, and possibly surface hoar. This sugary soft snow has been reactive in some snowpack tests and there have been some small slab avalanches noted on this layer.The lower snowpack is generally considered strong.

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