Boletín de aludes

East Slopes North

Northwest Avalanche Center
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Peligro de aludes

Sat
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 6 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Dangerous conditions exist due to recent snowfall and strong winds. The snowpack is complicated and variable. Many slopes may be nearing a tipping point, and need only the weight of a person to initiate a wide and surprising avalanche. Friday is a good day to avoid all large open slopes steeper than 30 degrees at all elevations.  

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    2

    Persistent slab avalanches can catch even the most experienced backcountry travelers by surprise. They can break widely around terrain features and be triggered from lower angle slopes. There is lots of variability in the snowpack, and we don't have a good handle on it, especially while we are in the midst of a storm cycle such as this one. In any case, numerous reports of loud whumphing tell us that we may be reaching a tipping point, and the triggering of these slides may be fairly easy to do.  This instability dominates the way we think about, and plan to travel in the backcountry because all slopes steeper than 30 degrees are suspect. Look for a thin layer of weak snow above or below a crust roughly 14"-24" down from the surface. There may be a layer of buried surface hoar a few inches above this crust as well. Whumphing and collapsing of large sections of snow direct signs that the snowpack is unstable. 

    On Thursday an observer reported whumphing on Delancey Ridge, and snowpack tests indicated failure on weak snow below the crust at low elevations (South at 3,900ft). On Wednesday multiple observers experienced whumfping collapses, signs that a  persistent slab problem may be primed to wake up.  Dig down to look for weak sugary snow above a firm crust at all elevation bands.  Stiff, wind drifted slabs may be found at upper elevations. Places where firm, drifted snow covers steep slopes will be especially important to avoid on Friday, as any slide triggered in wind stiffened snow has the potential to be a much larger avalanche.

    Widely propagating crowns such as this are characteristics of persistent slab avalanches.

  • Storm Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2

    Another incoming storm will begin to lay down a new blanket of snow. Temperatures are forecast to warm up as it comes in, perhaps making for an upside-down feeling snow surface. Steer around any open slopes greater than 35 degrees where you find more than 6” of new storm snow. You can use small slopes and hand pits to see which storm layers fail. There is potential for any shallow avalanche in the surface layers to step down to the crust and become a much larger slide. Storm slabs may become easier to trigger during intense snowfall and warming temperatures in the afternoon. 

    Small slabs on steep convex rolls such as this are signs of storm slab instabilities.

Avalanche Discussion

A solid round of snow fell in the mountains of the East North Zone on Wednesday night. Washington Pass picked up about 10" of snow with 0.7" of water equivalent and the station at Mazama picked up 6" with 0.5" water equivalent.  Winds were moderate from the southwest following the snow, and likely caused notable drifting at upper elevations. The active weather pattern will continue, and the snowpack will get deeper with each storm. 

The snowpack and resulting avalanche danger likely varies greatly across the zone. A translucent freezing rain crust from December 9th can be found below 5,000ft and east of Washington Pass. Above and west of there, the 12/9 presents as more of a thicker and rough melt freeze crust. 

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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