Bulletin d’avalanche

Kootenay Boundary

Mar 17 – 18, 2016Avalanche Canada
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Archivé · expiré 11 years ago

Danger d’avalanche

Sat
Sun
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Points saillants

All bets are off this weekend as very warm air spills into the region sending the freezing level well into the alpine. Rapidly rising temperatures may initiate large natural avalanches. Choose very conservative terrain free of overhead hazard.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    3–5
    Deeply buried surface hoar down about one metre continues to be triggered by light additional loads like a single skier or rider. Forecast strong solar radiation and warm daytime temperatures are expected to increase the likelihood of triggering.

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible - Likely
    Taille
    1–4
    Recent storm slabs and cornice growth continue to be a concern for human triggering. Forecast strong solar radiation may increase the likelihood of triggering large avalanches.

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–3
    Forecast strong solar radiation may result in loose wet snow releasing naturally from steep terrain or easily triggered by skiers and riders. Loose wet avalanches may step down to a buried crust or a deeper persistent weak layer.

Confidence

Moderate

Weather Forecast

The ridge remains in place Friday offering one last day of seasonal normal temperatures before southwesterly flow injects a substantial amount of warm air into the region Saturday and Sunday. FRIDAY: Freezing Level climbing to around 1500 m, returning to valley bottom overnight, light variable winds, no significant precipitation expected. SATURDAY: Freezing level starting at valley bottom climbing to 2500 m in the afternoon, moderate southwest winds, no precipitation. No overnight temperature recovery expected. SUNDAY: Freezing level holding at 2500 m, moderate southwest winds at ridge top, no precipitation expected. Increasing cloud cover will likely trap warm air leading to a greenhouse situation.

Avalanche Summary

It's been a very active period with numerous large natural and human triggered avalanches being reported over the last few days.  On Wednesday a skier remote triggered a cornice failure from a few meters away on a north/northeast facing slope around 2100 m in the Rossland range.  When the falling chunks of cornice impacted the slope below it triggered a very large (size 3) avalanche that ran on the March 6th crust.  Natural cornice failures were also reported.  A second skier triggered avalanche (size 2) was reported on a northeast facing feature near 2000 m.  Numerous loose wet avalanches to size 1.5 were also reported from solar aspects.  (Those with a south facing component.)  On Monday a sleddder triggered a size 2 avalanche on a north facing feature at 1900 m failing on the late February surface hoar which resulted in a fatality in the Mt. Mackie area southwest of Castlegar.

Snowpack Summary

The recent storm snow is 40 to 60 cm deep and continues to settle above a mix of crusts at treeline and below. In some drainages these storm slabs may be sitting on a thin crust that was initially buried on March 11th. A second curst, (the early March melt/freeze crust) can be found down 50 to 80 cm. The late February (Feb 27th) persistent weak layer of buried surface hoar down 70 to 120 cm continues to result in large avalanches. I suspect that this weak layer is more prominent on northerly (shaded) aspects at and above 1700 m. This surface hoar layer may be associated with a crust on solar aspects. With forecast sun and strong solar radiation, triggering this deep weak layer may be more likely. Watch for moist or wet surface snow as a sign that solar radiation is strong and deep weak layers may become reactive.

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