Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

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

In sintesi

On Thursday, you may be able to trigger small avalanches in freshly fallen snow on slopes 35 degrees and steeper. Avalanches at mid and upper elevations may be bigger and easier to trigger. Watch for recent avalanches or test slopes that slide easily as signs that you should stick to lower-angle terrain.

Problemi valanghivi

  • Storm Slabs

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

    Storm slab avalanches will be most likely and consequential at mid to upper elevations. While there's a chance you may be able to trigger one below treeline, they will generally be unlikely there. You could trigger avalanches within the new snow or at the interface of old and new snow. If you find unstable snow, stick to lower-angle slopes under 35 degrees. Steer around convex roll-overs and steep, unsupported slopes. Use caution in and around terrain traps, where avalanches could have serious consequences.

    Expect a dusting of another couple of inches Wednesday night, adding up to 5-8" in the past two days. Warming temperatures may bring cohesion to the recent snow, possibly forming a slab or even small wet avalanches in the low valleys. Above treeline, you may encounter subtle drifting and stiffer, wind-affected snow. Cracking and stiff feeling snow are all indicators. Use caution on leeward wind-loaded slopes over 35 degrees. On any slope, you can use quick snow pits and small, inconsequential test slopes to check if the snow slides easily. Look for a potential poor bond at the new/old interface where observers have reported weak surfaces, including surface hoar below 6,000ft. 

    (12/28/2020) An example of a snowboarder-triggered avalanche in recent snow on Shuksan Arm near Mt Baker ski area (NE, 5400ft). Photo: Colin Wiseman

  • Persistent Slabs

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

    While triggering a persistent slab avalanche is unlikely, the consequences are serious. There's still enough uncertainty that we can't rule out these avalanches. They can be dangerous and surprising and can catch even the most experienced backcountry travelers. 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.

    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 decreased.  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 Wednesday, observers reported about 6 inches of new snow overnight. The new snow was light and uncohesive except near ridgtops. 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 surfaces 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. 

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.

Regioni coperte