Bulletin d’avalanche

Northwest Coastal

Dec 9 – 10, 2017Avalanche Canada
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Archivé · expiré 9 years ago

Danger d’avalanche

Mon
Tue
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Points saillants

Forecast freezing levels and precipitation amounts are highly uncertain for Sunday. Pay close attention to how much rain or snow falls in your area and be prepared to back off to simple terrain.

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–3
    Fresh storm slabs will begin to build as a storm pulse brings snowfall with strong winds. Poor bonding may occur at the surface, so slabs may be touchy. Expect thicker, more dangerous slabs in coastal areas and on lee aspects.

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible - Likely
    Taille
    1–2
    Rain on Sunday may cause small loose wet avalanches to occur, mainly in steep terrain and where rain or moist new snow accumulates.

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely - Possible
    Taille
    2–3
    Weak layers buried near the base of the snowpack can't be dismissed while new snow or rain load the surface. Releasing a thick storm slab or wind slab in the right location may provide enough of a trigger to step down a deep early season weakness.

Confidence

Low - Timing, track, or intensity of incoming weather system is uncertain on Sunday

Weather Forecast

Saturday night: 5-20cm of new snow with rain at lower elevations / Strong to extreme southerly winds / Freezing level at 1800mSunday: 5-30mm of precipitation / Strong to extreme southerly winds / Freezing level at 2400mMonday: Clear skies / Strong to extreme southerly winds / Freezing level at 2400mTuesday: Trace amounts of new snow / Light variable winds / Freezing level at 1200m

Avalanche Summary

On Friday, warm temperatures and sunshine initiated numerous loose wet avalanches to Size 1.5 on steep solar aspects in the alpine around the Terrace area. Warming also triggered a few deep persistent slabs to size 3 out of steep south facing alpine terrain. Basal facets were though to be the culprit in these events. Looking forward, forecast snow and wind will likely promoted a round of storm slab activity in higher elevation terrain. In areas where rain falls, loose wet avalanches may continue to run in steep terrain .Avalanche and snowpack data is extremely sparse at this time. Please submit your observations to the Mountain Information Network. (MIN)

Snowpack Summary

Up to 5mm of rain fell in the Skeena corridor on Friday night. At higher elevations I suspect snow fell and was shifted by strong winds into wind slabs in lee terrain. In the Bear Pass area where temperatures were cooler, around 15cm of new snow fell down to near valley bottom. These accumulations overlie melt freeze crusts and possibly surface hoar.Another layer of large surface hoar that was recently observed in the Shames area is now buried about 15 cm below the surface. Information on the distribution and reactivity of this layer is limited. Below it, storm snow received last week is gradually settling above a 5-10 cm thick crust (November 23) down roughly 70-100cm. Another layer of surface hoar (November 11) continues to be observed down approximately 140 cm in the Bear Pass area, showing some signs of improved bonding. The widespread crust/facet interface that was buried at the end of October can now be found 90-160 cm deep. The base of the snowpack is reported to be a mix of facets and melt-freeze crusts..

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