Bulletin d’avalanche

Northwest Coastal

Jan 17 – 18, 2017Avalanche Canada
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Archivé · expiré 10 years ago

Danger d’avalanche

Wed
Thu
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
4 · Fort
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Points saillants

The storm continues, and avalanche danger is HIGH at all elevations.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely - Possible
    Taille
    1–3
    It is still possible to trigger avalanches on buried weak layers (Dec 25, Dec 30, Jan 5th, Jan 12th surface hoar) ... or have a smaller avalanche 'step down' and trigger deeper instabilities.

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–3
    Lots of storm snow sits on a complex mix of wind slabs, surface hoar and facets. Conservative terrain use is essential!

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2
    Watch for moist or wet snow below treeline that may be easy to trigger or release naturally due to rising freezing levels and rain on previously dry snow.

Avalanche Summary

I expect that a natural storm slab avalanche cycle is on-going in the south of the region near Terrace and also near Kitimat. The peak of the storm may have already passed through the north of the region. We have not had any reports of persistent slab avalanches, but that may be due to poor visibility and travel conditions.

Confidence

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

Weather Forecast

Storm continuing overnight with strong southwest winds and 15-30 mm of precipitation by morning. Freezing levels will be variable across the region, likely 1200 metres in areas that receive the most precipitation in the south and around 500 metres in the north. Storm continuing on Wednesday with strong southwest winds and up to 20 mm of precipitation in the south with freezing levels around 1000 metres. Storm weakening on Thursday with moderate winds and 5-10 mm of precipitation. Clearing and cooler on Friday with light winds.

Snowpack Summary

We've had a significant warming trend since the arctic outbreak, and a large storm snowfall gradient (30-40cm in the south ; 60-80cm near Stewart). The new snow fell with moderate to strong SW winds, and formed touchy soft slabs and wind slabs. Expect this new snow to bond poorly to all the windslabs (and a spotty layer of surface hoar and facets buried Jan 12th) that formed during last week's arctic outbreak conditions. The older wind slabs sit on a variable interface composed of hard wind slabs, weak surface hoar (Jan 5/6 layer) and faceted snow. If you're starting to think it's a dog's breakfast, you're right! With the recent new snow loading, the deeper slabs have remained reactive, especially on southwest facing features near ridge crests. Deeper in the snowpack, the Christmas surface hoar layer (buried 70-120 cm) is still preserved in some southern areas and has been reactive in sheltered areas and steep open features at treeline and below treeline. Lower elevations (below treeline) have moist snow below 1000m elevation, making for heavy and difficult riding.

Régions couvertes