Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

Be leery of wind-loaded terrain where triggering an avalanche is more likely.  Steer around slopes that contain new drifts or firm, hollow-feeling snow. Further south in the zone, slabs may be larger, increasing the potential for failures on buried weak layers.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    Due to a flip-flopping wind direction, you may find wind slabs on various aspects on Saturday. Fierce east winds on Wednesday and Thursday resulted in what are now, older, firmer, and potentially larger slabs. Meanwhile, shallower and softer slabs may have formed as the wind switched westerly on Friday and Saturday. Any of these could overlay soft, weak snow from earlier this week, allowing them to fail easily. Or they could sit on a subtle melt-freeze crust on slopes that typically receive direct sunshine, giving them a good sliding surface.

    It sounds complicated, but your management is relatively simple. Use visual clues such as textured surfaces, fresh cornices, or pillow-like drifts to identify wind-loaded features to avoid. Regardless of direction, the wind tends to deposit snow on leeward ridgelines, convex rollovers, the base of rocks/cliffs, or the sides of gullies/chutes. These are the most likely locations to encounter slabs on Saturday. 

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2

    Our persistent weak layers should get tested this weekend as we incrementally load them through snow showers and wind. They've already survived an intense east wind event without any reported persistent avalanches. But the big shot of water is in store for Saturday night/Sunday. It remains to be seen if this storm will be enough to wake these layers up and produce avalanches. In the meantime, your best mitigation tool is still avoidance of large open slopes, especially if they're wind-loaded.  Discuss the consequences of a slide with your partners if you are considering non-wind-loaded steeps on the shaded half of the compass. Your default should be to choose simpler, smaller, and lower-angle terrain. 

    (2/1/2025)

    This intentionally triggered persistent slab in the West South zone propagated the entire width of the feature. It failed on facets over a thin crust. ENE, 6200ft, SS-ASc-D2-R3-O, 20-24 in deep, 200 ft wide.

    Photo: Dallas Glass

Avalanche Discussion

The wind has been the major driver of avalanche potential this week in the West South zone. First, the intense easterly winds on Wednesday and Thursday reached into the 60 mph range and easily transported snow onto leeward slopes, resulting in shooting cracks and sensitive avalanches. Then, after a brief lull on Friday morning, the direction switched westerly. The winds started to crank again, particularly in the southern half of the zone. White Pass was back to gusting into the upper 50s on Friday afternoon, and over a foot of snow fell on our sister volcano, Mount Hood. The snow surface is now variable, with a mix of wind-affected snow, sun-crust, and well-settled powder. 

As mentioned in the persistent slab problem, this weekend may put our buried weak layers to the test. The January Drought Layer (JDL) and 1/10 complex are a few feet below the surface and have been dormant for roughly the past week. Snowpack tests and investigations by NWAC forecasters indicate that these layers have not healed much during this cold snap. They are likely awaiting the right amount of load to start tipping the scales and wake up. The last reported activity on these interfaces was a whumpf in the Crystal area on Monday. We'll see what Saturday brings, but as the snow stacks up in the afternoon/evening, we'll be thinking about increasing the likelihood of triggering heading into Sunday. Due to more inputs over the past few days, the southern half of the zone may be inching closer to potential slides on this layer than further north. Regardless of your location, if you hear whumpfing collapses or see widely breaking avalanches, dial your terrain selection way back, and please let us know by submitting an observation.

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