Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

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

You may see natural avalanches, especially at mid and upper elevations Friday during periods of heavy snowfall and strong winds. Choose simple terrain where you can easily avoid areas where avalanches can start, run, and stop. The stormy weather could make it hard to navigate and manage your risk. 

Problemi valanghivi

  • Wind Slabs

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

    Very strong winds should easily build thick new slabs at all elevations on Friday. We expect the continued loading to overburden many slopes near and above treeline causing them to avalanche naturally. With such strong and swirling winds, you may encounter wind slabs on a variety of aspects and features. You could see wind loading in the trees, along the sides of gullies, and even on subtle mid-slope features. Keep it simple Friday and stay off open slopes greater than 35 degrees, and out of avalanche terrain entirely at mid and upper elevations. 

    While the wind really headlines this storm, heavy precipitation rates may form slabs even in sheltered areas. Just because you’re out of the wind, doesn’t mean you’re out of danger. Soft storm slabs may trigger easily within the new snow or at its base. Thin crusts and weak grains found at this interface could allow them to trigger remotely or propagate widely. Steer around all slopes greater than 35 degrees even at lower elevations.

    (2/23/2021) This slab was triggered by an intentional cornice drop in Gunsight bowl near White Pass on Tuesday (2/23). The slab was 18" deep. [NE aspect 6300'. SS-ACc-D2-R2-I]

  • Deep Persistent Slabs

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

    The recent atmospheric river significantly tested the deeper layers in our snowpack. Very thick and wide crowns observed on Wednesday indicate that several avalanches failed naturally on these layers during this storm cycle. Crystal Mountain Ski Patrol also triggered an avalanche on a deep persistent layer. While it may prove difficult to trigger these weak grains, any resulting avalanche would become very large and destructive. You could see isolated deep slabs fail during periods of heavy precipitation or if a smaller slide steps down into the older snow. Stay out of the runout zones of larger avalanches paths as this storm plays out. 

    (2/23/2021) This avalanche was released sympathetically during control work by Crystal Mountain Pro Patrol on Tuesday (2/23) and was confirmed to have run on the Mid-January crust/facet combo. It was 5 feet deep and over 100 feet wide. [E aspect, 5700'. Photo: Robin Pendry]

Avalanche Discussion

Yet another significant winter storm will quickly bring 1-2.5ft of snow and very strong winds to locations around the West South by Friday afternoon. This could result in several rounds of natural avalanche activity especially near Mt Rainier, Mt St Helens, and Mt Adams where you may encounter heavier snowfall rates. This will add to the snow above the 2/25 interface where you could find a thin crust, graupel, or even surface hoard depending on your aspect and location. If avalanches fail at this interface they could trigger very easily and act in more surprising ways. 

Deeper persistent weak layers continue to linger in the snowpack. While it can be easy to downplay this current storm in light of recent events, it’s still a significant load over a short period of time. We don’t know how these deeper grains will respond. The most worrisome persistent layer continues to be the mid-January facet/crust. This layer sits 5-10 ft below the surface depending on your location. 

Cornices grew very large and overhung during the recent storms. As they continue to grow some of them will fail and could act as very large triggers on the slopes below. Use extra caution if you travel along ridgelines where cornices could fail much farther back than you might anticipate. 

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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