Bulletin d’avalanche

West Slopes South

Northwest Avalanche Center
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Danger d’avalanche

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

Much of the West South zone sits right in the bullseye of a major winter storm that could bring our first significant avalanche cycle of the season. Expect particularly dangerous conditions in the morning as heavy snowfall and strong winds continue to impact the mountains. Make sure you choose a plan that allows you to easily identify and avoid steep open slopes that can produce avalanches.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2

    Moderate to strong winds will easily transport the low-density snow and build slabs on the lee side of ridgelines, exposed features, and cross-load mid-slope gullies. Because any of these avalanches could easily grow large enough to bury and kill you, this won’t be a day to try and poke around the edges of this problem. Let visual clues help you anticipate which aspects and features likely hold wind slabs. Look for sharp cornices, drifts, and textured surfaces to highlight terrain you want to avoid. Shifting winds, particularly near Crystal and White Pass, could further complicate this issue and form wind slabs on a variety of aspects.

    (11/28/2022) Snow (or lack there of) in the trees can serve as a great clue to help you locate potentially wind loaded slopes. Photo: Dallas Glass

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    All the ingredients exist for sizable storm slabs Wednesday: significant new snow, high precipitation rates, and fluctuating temperatures. Just because you’re out of the wind doesn’t mean you’re out of danger. Any steep open slopes should be suspect. Use simple observations like handpits, uptrack tests, and small slopes to gather information about the new snow and its bond to the old surface (11/29 interface). When you see layers fail consistently and cleanly expect storm slabs in nearby terrain. 

    While we don't have any direct observations, weak snow may exist at the 11/29 interface. Very cold temperatures and weak surface snow prior to this storm could produce a very poor bond and allow avalanches to fail at the base of the storm snow.

    (11/26/2022)

    Quick hand pits while you travel can give you an indication of how new snow has bonded to old snow surfaces or if it has come in upside down.

    Photo: Andy Harrington

Avalanche Discussion

The West South zone will take quite the hit from this storm. Locations on Mt Rainier, Mt St Helens, and Mt Adams could experience locally very dangerous conditions. This may include more widespread and larger avalanche cycles in these locations. Consider simply avoiding any area where an avalanche could start, run, or stop if you plan to travel to these mountains. 

The dynamic nature of this storm makes forecasting and timing quite complicated. We anticipate the bulk of the precipitation/wind, and thus avalanche activity, to occur overnight Tuesday into the wee hours of Wednesday morning. However, if the storm lingers longer than expected, or if you plan to head out for an early dawn-patrol, you may encounter more dangerous conditions. Fortunately, we anticipate avalanche activity to remain with the new snow at or above the 11/29 interface. 

To further complicate the matter, this is a particularly cold storm for November and some of our common Cascade rules of thumb may not apply. Don’t be surprised if you see snowfall totals exceed expectations given the precipitation water amounts. You may even see the snowpack act a bit differently than normal. 

Even with all the new snow, plenty of thinly buried obstacles exist. Give yourself time to navigate these early-season hazards.

Régions couvertes