Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Wed
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

The avalanche danger has eased, continue to practice safe travel protocols. You may trigger a small windslab in extreme terrain above treeline. Large persistent slab avalanches are unlikely, though still worth consideration in shallow, rocky terrain. Expect an increase in avalanche danger going into Wednesday with the arrival of a potent storm. 

Problemi valanghivi

  • Wind Slabs

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

    You may find small wind slabs scattered in upper elevation, wind exposed terrain. Look at snow surface texture and feel for stiff snow over weaker snow to identify wind slabs. Use test slopes to check how well these slabs are bonding. Avoid consequential terrain steeper than 35 degrees if you find instability such as shooting cracks or propagation with test results. You may be most likely to trigger one of these on very steep and unsupported slopes above treeline.

    Example wind slab near Cutthroat Pass, photo from last season.

  • Persistent Slabs

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

    Persistent slab avalanches are still on our radar due to a weak layer of sugary snow that sits above and below a thin crust from early December. This structure continues to warrant respect, even though the chances of initiating a slide have significantly decreased. The consequences of triggering a slide on this layer are high, because it could easily be large enough to bury or kill you. Keep a distance from large slopes that are steeper than 35 degrees, especially unsupported and convex slopes. Avoid hanging out, and grouping up in potentially consequential runout zones. This may include sparsely treed slopes or other terrain traps. Watch for obvious signs of instability like whumphing collapses, or cracks shooting through the snow.

    The layer of concern is a thin weak layer of small facets (and in places surface hoar) buried about 2-4 feet below the surface. Near the top of Washington Pass, this weak layer will be sitting on an icy crust. Further east in the zone, the crust has decomposed into a mix of melt forms and weak grains. At lower elevations, there's less concern for triggering this layer.

    (12/23/2020) Persistent slab that likely ran on the Early December Crust. West facing slope in the trees at 6,800ft near Silverstar Mountain.

Avalanche Discussion

On Sunday an observer in Cutthroat drainage found sudden test results within recent storm layers down about 12" and 24" on a northeast aspect at 6,500ft. Storm totals since Christmas are around 3-5" of settled snow. Previous surfaces were a mix of decomposed grains and wind packed particles in some areas, and weak snow over slick bedsurfaces in others. Observers have noted that many slopes ran during the widespread avalanche cycle of December 21st. In some cases, this has allowed folks to cautiously step out and travel onto slopes safely, if they know for certain that it already slid. The new snow may obscure evidence of where these slides have run, creating continued uncertainty. 

A potent storm looks to arrive overnight Tuesday into Wednesday, increasing the avalanche danger significantly. 

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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