Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Mon
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

The likelihood of triggering an avalanche post-storm has decreased but is certainly not eliminated. Uncertainty surrounds conditions on the volcanoes and the southern half of the zone. Be diligent in making your slope scale assessments and when choosing terrain.

Problemi valanghivi

  • Wind Slabs

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

    The most likely location for you to trigger a slab avalanche should be in wind-loaded terrain on Sunday. Look for features that look “fat” with pillow-like drifts compared to the surrounding area near ridgelines, confined gullies, or on convex rollovers. You may see other visual clues such as textured surfaces or sharp cornices in the nearby terrain that can help key you into which way the wind was blowing and thus wind-loaded aspects. Using small test slopes or performing uptrack tests in benign terrain can help you identify how the recent storm snow is reacting to your weight as a traveler. If you notice cracking or blocks of snow failing easily during your tests, choose an alternate path avoiding wind-loaded slopes.

    In areas further south such as the volcanoes, you may still encounter unstable snow on any slope over 35 degrees. Use quick hand pits along with those same test slopes and uptrack tests to check for potential weak points.

    (3/25/2023)

    In the neighboring Snoqualmie Pass zone, multiple human-triggered slabs failed near the base of the new storm snow. [N 4800]

    Photo: Bryan Eastes

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Sunshine and temperatures are forecasted to slowly increase on Sunday which could be enough to kick off some Wet Loose avalanche activity. That said, temperatures aren’t skyrocketing and we’re not expecting full sun, so this problem may not materialize. We have a big zone, so you’ll need to keep an eye on the weather and how the snow surface is changing throughout the day wherever you’re out playing. If the snow is getting wet and sticky or the sun is out for a prolonged period of time, make a judgment call on if you should head for shadier slopes to avoid this hazard. If you see new rollerballs or fan-shaped avalanche debris due to solar input, then the decision is likely made for you. You’ll know it’s time to head for sun-protected slopes keeping aware of hanging blocks of snow such as cornices or glide cracks above you.

    (3/17/2023)

    Example: rollerballs and Wet Loose avalanches on a steep sunny slope from our last post-storm warm-up. Note how they originate at a point near rocks and trees.

    Photo: Rachel Gronvold

Avalanche Discussion

We’re coming out of a multi-day storm that dropped roughly 1.5-2 feet of snow on the volcanoes and southern portions of the West South zone. In areas further north and closer to the crest such as Crystal Mountain, considerably less snow fell during the event (closer to 7 inches). On Sunday, you may see a few showers pass through here and there, but the precipitation is largely finished. You’ll need to manage lingering storm instabilities confined to the new snow during your travels and keep an eye out for changing conditions due to solar input as noted above.

Observations are extremely limited from the West South zone on Saturday. Avalanche professionals in the Crystal Mountain area reported a couple of inches of new snow that was running far on the underlying sun crust when triggered by skiers on steep slopes. No information was relayed from the volcanoes or the southern half of the zone where the bulk of the storm hit. If you have been out in these areas or are planning on going on Sunday, please submit an observation. 

In the neighboring Mount Hood zone, similar accumulations were received during the recent storm as our southern volcanoes. Avalanches as large as D2.5 were triggered during mitigation work by Meadows Pro Patrol on Saturday. You may want to consider reading the Hood forecast to get a feel for how this storm has played out further south if you’re planning on traveling to Mount St. Helens or Mt. Adams on Sunday. In the neighboring Snoqualmie Pass zone to the north, multiple human-triggered avalanches occurred on Saturday within and at the base of the new storm snow.

Prior to the storm, mostly warm and sunny weather impacted the West South for the majority of the past week. A surface crust formed on most aspects and elevations. The caveat is high-elevation northerly terrain where dry soft snow survived and possibly faceted (weakened) during this spell. Be sure to check the bond to the old snow surface (3/22 interface) throughout your travels. All avalanche activity is expected to occur at or above this interface on Sunday.

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