Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Sat
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

On Friday, another round of rain and high-elevation snow could result in wet avalanche activity. Limit your exposure to overhead hazards and slopes that are wet and weak. Although unlikely, deep layers in the snowpack could still fail until a new surface crust sufficiently bridges them. 

Problemi valanghivi

  • Loose Wet

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

    Rain could reinvigorate wet avalanche potential on Friday. The most likely scenario will be a few small loose avalanches in areas where Friday's rain destabilizes Thursday's snow. In isolated locations, they could gouge down into older snow layers and start to grow in size. Although unlikely, the more dangerous scenario will be if water percolates into the snowpack and wet slabs, glides, cornices, or other shed-style avalanches fail. These larger and more unpredictable slides should have you choosing travel routes that minimize your time spent with overhead hazard. If the snow surface is wet and weak, put wet avalanches on your radar.

    (2/11/2024)

    Example: Rollerballs and other wet loose avalanche activity coming out of steep rocky terrain during a rain storm earlier this season.

    Photo: Andy Harrington

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–3

    Facets on or just above the Early February Crust have had our eye for much of the past month. Avalanche activity has been feast or famine over this period, with many widely propagating and deep avalanches reported.  This past week's warmup and sunshine allowed plenty of visibility into the mountains, and multiple new crowns were spotted. Although not all of these avalanches are confirmed to have failed on our deep persistent layers, it's a good bet that most of them did. Recent snowpack tests indicate that the setup responsible for these avalanches is still in place, but is finally showing some signs of healing. The significant swings in the weather, loading from other avalanches, and these encouraging test results have us thinking it is unlikely to trigger one of these slides as a human traveler. That said, a cornice collapse or other avalanche could do the trick in isolated locations. If one were to fail, it would likely be deep, wide, and deadly. 

    (3/18/2024)

    A widely breaking avalanche in Mount Rainier National Park. It likely occurred on 3/18 and may have broken on persistent weak layers.

    Smaller wet avalanches can be see in the foreground. 

    Photo: Crystal Mountain Pro Patrol

Avalanche Discussion

We'll have to wait at least another day to freeze up the surface and put our wet avalanche concerns to bed. Although they're trending toward unlikely, we can't entirely write them off while it's still warm and raining. Friday should be a notch warmer than Thursday, with a higher rain line. You'll likely encounter some fresh snow at the highest elevations or on the volcanoes. Winds should be lighter on Friday, but keep an eye out for shallow pockets of wind-drifted snow in confined gullies or on leeward slopes.

On Thursday, the West South picked up anywhere from 2-4" of new snow at mid to upper elevations, accompanied by some wind. White Pass Pro Patrol reported that the new snow drifted into shallow wind slabs. As temperatures rose throughout the day, the new snow moistened. 

New snow is a significant change from what the snowpack has been through over the past week. During that time, hot and sunny weather resulted in a substantial loss of snow and a widespread wet avalanche cycle. The whole spectrum of wet problems has been observed during this timeframe - loose, slab, cornice, and glides. Percolation channels, layers of pooling water, and moist grains now dominate much of the snowpack, making it well-suited to handle the incoming rain.

Travel conditions have worsened over this period as well. Tree debris, open holes and creeks, and exposed ground have reappeared. Give yourself extra time to navigate these hazards.

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