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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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Wednesday should be a return to more winter-like weather around the West South zone. Despite this change, dangerous avalanche conditions will persist. You will likely need to manage both dry and lingering wet slabs if you venture into the mountains. As you recalibrate your mindset to the new landscape, keep things simple by avoiding open slopes over 35 degrees.

Problèmes avalancheux

  • Wind Slabs

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

    Strong to extreme winds will continue on Tuesday evening and will easily be strong enough to move around newly fallen snow into Wind Slabs. These slabs should be thicker, and possibly more reactive as you ascend in elevation. You are most likely to find them in exposed areas near the leeward side of ridgelines or on convex slopes. Freshly built cornices, textured surfaces, or fresh drifts behind natural objects can help you identify potentially unstable slopes to avoid. 

    In more protected areas, we expect new snow to bond fairly well to a generally warm and wet surface. That doesn’t mean that stability is a guarantee, however. Take some time to use uptrack tests, hand pits, or small test slopes to see how the new snow has bonded or if it has come in upside down (heavy snow over weaker snow). When in doubt, avoid slopes over 35 degrees whether they are wind-loaded or not. 

  • Wet Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1.5–2.5

    It may take some time for the recent rain to drain out of the snowpack and put our wet problems to bed. While the cooling temperatures should help to kick off this process, liquid water can linger in the snowpack and produce avalanches long after the rain has stopped. You won’t be able to predict when these slides will occur, so your best option is to recognize the terrain where they’re more likely and avoid it. You should be suspect of open slopes over 35 degrees or areas where hanging blocks of snow linger on rocks and cliffs. 

    (12/26/2022)

    This very large avalanche was triggered by the Gazex Exploder seen near the top of the photo. It propagated almost the entire length of the ridge and released as one cohesive slab. It is suspected to have failed on the 11/22 weak layer. [Powder Bowl N/NE 6900']

    Photo: Crystal Mountain Pro Patrol

Avalanche Discussion

It was another wet and wild day in the West South zone, with areas closer to the crest averaging another 2” of water, give or take. We lost the Paradise weather stations due to a power outage, but they were on track for even higher water numbers. NWAC stations at Crystal and White Pass recorded gusts into the 80s and 90s and a few inches of snow (~3-4”) were recorded at mid to upper elevations as temperatures finally started to cool. This general cooling trend should continue overnight on Tuesday into Wednesday as another shot of heavy precipitation and strong winds impact the zone, delivering mostly snow as opposed to rain. It will likely still be quite stormy in the morning hours on Wednesday before the weather starts to ease. 

As this transition away from warm and wet continues, the snowpack should start to refreeze and stabilize from the top down. How long this process takes is unknown at this point, but it could take some time. This is a slow cooldown, we’re not exactly being thrown back into the freezer. 

No new avalanches were reported to us on Tuesday. White Pass Pro Patrol reported that the new snow was bonding fairly well to the rough snow surface and that winds were easily moving the new snow around in exposed areas. Both White Pass and Crystal Patrols reported standing water on the surface of the snowpack in the morning hours and that it was a generally stormy day. This is on the heels of Crystal getting very large avalanches during their mitigation work on Monday. Multiple very large slides propagated widely and broke 3-5 feet deep when triggered with explosives. They are suspected to have failed on a weak layer from late November (11/22). Over the weekend, Mount Rainier Rangers reported multiple natural Wet Slab avalanches well below treeline along the road to Paradise.

If you decide that Wednesday is your day to return to the mountains, please help our general understanding of the conditions by letting us know what you see. There is a lot of uncertainty around what happened during this cycle and how conditions are shaping up as we transition. What we do know is that whenever you do make it back out there, the mountains will look a lot different than when you last visited.

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