Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
3 · Marcato
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In sintesi

Very dangerous avalanche conditions are expected to continue on Saturday as new snow and strong winds load a weak snowpack. This weak snowpack has consistently produced avalanches for over a week and is not going to heal quickly. Let nature do its thing and stay out of all avalanche terrain.

Problemi valanghivi

  • Persistent Slabs

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

    Surprising avalanches have been easily triggered, propagated widely, and ran quickly in many areas of the West South this past week. Some of these slides were triggered from long distances away or stepped down into older, deeper layers of the snowpack. A weak snowpack structure has been observed throughout the zone, even in areas that have not yet produced these avalanches. There are currently two crusts within the snowpack that have weak snow grains sitting above or below them. With continued high precipitation rates on Saturday and more load added to stress these layers, we expect more of these scary and unpredictable avalanches to follow. Stay away from all terrain where avalanches can start, run, or stop. 

    (2/5/2021) This avalanche was remotely triggered in backcountry terrain just outside of the Crystal ski area. Similar to other recent slides, it failed on facets just above the 1/13 crust. 60cm deep, 150' wide. 5200' ESE aspect. Photo: Crystal Mt Ski Patrol

  • Storm Slabs

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

    If you took away the deeper instabilities and threw us back into what we perceive as normal Pacific Northwest conditions, this storm would still be capable of creating plenty of avalanches on Saturday. Snowfall is expected to increase throughout the day with a slight bit of warming in the afternoon hours. These fluctuating snow levels combined with strong winds should create multiple potential weak interfaces in the recent storm snow. Snowfall should be more significant on the volcanoes while winds should be more significant closer to the crest, creating a little variability. Regardless of where you find yourself, any avalanche failing on these layers could act as a trigger for those deeper persistent slabs. Even if you suspect that a persistent issue does not exist in your area, you should stay out of avalanche terrain as this storm runs its course.

    (2/5/2021) The upper snowpack contained multiple density breaks and "normal PNW" weaknesses above the persistent layers at Paradise on Thursday. There should be even more from Thursday night and Saturday's storms. Triggering one of these layers could cause slabs to step down to those deeper and scarier persistent layers.

Avalanche Discussion

Unlike Thursday night’s storm, this storm should drop the bulk of its precipitation during the daylight hours on Saturday, increasing the hazard throughout the day. There are currently two layers of concern in the upper snowpack. The Mid-January Crust (1/13) contains weak snow grains on top of the crust and has been the culprit for much of the avalanche activity in the past week in areas such as Crystal, Mt. Saint Helens, and White Pass. This layer could be around 3-4 feet deep in some locations. The 2/1 crust is a bit closer to the surface and may be found closer to 2 feet down, with weak snow above and possibly below it. Although these weak snow grains have shown signs of healing in some locations, they have been the point of failure for avalanches all week long (up to size D2.5) and are very much in play. 

As we continue to receive new snow and wind, slab depth atop these weak layers will increase. Slopes that have reached their tipping point already could reload and produce another round of avalanches. More concerning may be slopes that have not yet reached their tipping point. Those slopes could finally reach that point on Saturday, producing large and deadly avalanches. Recent avalanches, persistent grains in the snowpack, strong winds, and heavy snow are all red flags informing you that the snowpack is unstable and needs time to heal. Continue to exercise patience and caution as this storm cycle plays out by staying away from avalanche terrain.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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