Bulletin d’avalanche

Northwest Coastal

Dec 5 – 6, 2017Avalanche Canada
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Archivé · expiré 9 years ago

Danger d’avalanche

Thu
Fri
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
3 · Marqué
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Points saillants

Rapid warming will deliver a stress test to the snowpack on Wednesday. Dial back your terrain selection and be keenly aware of overhead hazards.

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely - Very Likely
    Taille
    1–3
    The strength of bonding throughout the snowpack will be tested by solar input and warming on Wednesday. Recently formed wind slabs, mid-storm interfaces, as well as the crust under our recent storm snow are all candidates that could fail this test.

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible - Likely
    Taille
    2–4
    A lot of uncertainty exists around the reactivity of layers sitting near the base of the snowpack. Highly conservative terrain selection is warranted while the snowpack reacts to Wednesday's warming. Shallow releases may step down to deep weaknesses.

Confidence

Moderate -

Weather Forecast

Wednesday: A mix of sun and cloud. Light to moderate southwest winds. Freezing level rising from 2200 to 3300 metres over the day with a temperature inversion bringing alpine temperatures to around +5. Cooler temperatures at valley bottom.Thursday: Mainly sunny. Moderate south winds. Freezing level to a possible 3500 metres with alpine temperatures around +7. Cooler at valley bottom due to lingering temperature inversion.Friday: A mix of sun and cloud. Strong south winds. Freezing level dropping from 2700 to 1700 metres over the day. Alpine temperatures cooling from +5 to around +3 over the day as the temperature inversion breaks down.

Avalanche Summary

Reports from the Bear Pass area on Monday showed isolated wind slabs releasing naturally to Size 2 from steep, north-facing alpine features. Looking forward to the warming that is forecast for the next couple of days, keep in mind that the strength of the bond between our recent storm snow and deeper buried crusts remains in question (especially at the basal crust). With an increasing possibility for failures at these deep interfaces, it is strongly recommended to take a conservative approach to route selection by traveling through low consequence terrain.

Snowpack Summary

Average snowpack depths in the region are roughly 100-150 cm at treeline elevations. This means that our recent accumulated storm snow (100-130 cm) forms the vast majority of our current snowpack. Strong winds (mainly southwest) over the course of the storm developed deep deposits of wind slab on leeward slopes. The recent snow seems to be settling quickly and sits above a 5-10 cm thick crust that was buried just over a week ago. The crust/facet interface that was buried at the end of October can now be found 90-160 cm deep. Recent snowpack test results have shown hard but sudden results on this interface. The strength of these two deep weak layers will be an increasing concern as the snowpack is forced to adjust to forecast rapid warming.

Régions couvertes