Bulletin d’avalanche

Northwest Coastal

Mar 11 – 12, 2022Avalanche Canada
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Archivé · expiré 5 years ago

Danger d’avalanche

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

Fresh snow forecast tonight and Friday will build reactive slabs, especially where snow sits over a crust or buried surface hoar. Watch for deeper slabs in wind affected terrain features.

Danger is highest in coastal areas, storm totals decrease further inland. 

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3

    New load increases the likelihood of triggering avalanches on deeper layers. Storm slabs in motion or cornice falls may affect these persistent weak layers. Use extra caution during heavy snow, rain or wind. 

    Two layers of weak surface hoar are buried, 5-20 cm deep and 25-50 cm deep, mostly found in treeline and low alpine features sheltered from the wind and sun. 

    A widespread thick crust is buried 60-100 cm deep. Avalanches on this layer will likely reach large sizes.

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely - Very Likely
    Taille
    1.5–2.5

    Strong west/southwest winds will build larger slabs around terrain features like ridge lines. Storm snow will be most reactive where it overlies a smooth crust, or surface hoar. 

    At lower elevations, precipitation may be mixed or fall as rain. Expect wet avalanches to be likely where heavy, wet snow exists - and where rain breaks down the crust. 

Confidence

Moderate - We are confident the likelihood of avalanche will increase with the arrival of the forecast weather. Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

THURSDAY NIGHT: Snow continues with 5-10 cm possible overnight. Strong southwest winds. Freezing levels mostly at valley bottom. 

FRIDAY: Cloudy, 10-20 cm of snowfall, heaviest in the afternoon. Strong to extreme southwest wind, alpine high -2 °C, freezing levels rise to around 1000 m.

SATURDAY: Another 10 cm possible by morning. Mainly cloudy, flurries continue with 3 cm possible, moderate southwest winds ease through the day, alpine high -3 °C, freezing level at 900 m. 

SUNDAY: A mix of sun and cloud. Isolated flurries possible. Moderate southwest winds. Freezing level around 800m. Alpine high -3. 

Avalanche Summary

This storm will bring fresh snow and strong winds - expect new slabs to be reactive to human triggers. 

On Wednesday several wind slabs were reported throughout the region. Small naturally triggered slabs were reported with a notable size 2 triggered by a cornice fall, see the MIN report for full details. 

Wind slabs have been sitting over a variety of surfaces, including a crust or surface hoar which has increased reactivity in specific features. A size 1.5 was triggered on Wednesday, on the mid February crust buried around 40 cm.

Over the last 10 days, a few size 1-2 persistent slabs have been triggered on the buried weak layers described in the snowpack summary section. Avalanches were mainly triggered on North through East aspects, between 1200 and 1800 m. Recent activity suggests they are becoming less reactive with the last reported avalanche on Sunday the 6th.

Snowpack Summary

New snow will fall on hard wind affected surfaces in most terrain features, and on a crust in sun affected slopes (observed up to 1750 m). A layer of surface hoar may be buried by the storm snow in isolated terrain that is sheltered from the sun and wind, new snow will be most reactive in these features. 

Low elevations may see mixed precipitation or rain, falling on a widespread crust observed on all aspects to 1000 m.

Several weak layers sit in the upper/mid snowpack that have been recently reactive. A layer of surface hoar buried early March is down 5-20 cm, preserved in wind sheltered terrain features at treeline. Another layer of weak surface hoar from late February is buried 25-50 cm deep, and is most prominently at treeline elevations. A thick crust from mid-February is buried 60-100 cm. The snowpack below is well consolidated.

Terrain and Travel

  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • As the storm slab problem gets trickier, the easy solution is to choose more conservative terrain.
  • Be careful as you transition into wind affected terrain.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.

Régions couvertes