Bollettino valanghe

West Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

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2 · Moderato
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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

Avoid wind drifted slopes 35 degrees and steeper at upper elevations, especially where an avalanche could carry you into rocks, trees, cliffs, or other obstacles. Watch for wet and weak snow surfaces on solar aspects as the sun comes out Friday. Use caution as the icy old snow surface below the recent snow is a good sliding surface for avalanches and still makes for slick and challenging travel conditions.  

Problemi valanghivi

  • Wind Slabs

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

    You can trigger an avalanche in wind drifted snow large enough to bury, injure, or kill a person. Pay attention as you transition into wind affected terrain and look and feel for sudden changes in snow surface texture and hardness. Fresh slabs rest atop variable surfaces including icy crusts and weak, sugary snow. These slabs developed with the moderate to strong winds we’ve seen since Tuesday. The wind caused a unique loading pattern, so you may find deposits in unusual locations and further downslope than you might normally look. Search for them around features such as in gullies or near rock outcroppings, and along ridges. Snow may appear smooth, pillowlike, or textured, and feel stiff and hollow. Avoid slopes steeper than 35 degrees where you find any of these snow characteristics.

    (1/26/2021) A human triggered wind slab on Mt Herman on a west aspect just below 6000ft. The avalanche broke 1-2ft deep, 25ft wide, and ran 200ft downslope. Photo: Francis Neff (West North Zone)

  • Loose Wet

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

    The recent cold, low-density snow will see sunshine for the first time this week with periods of clearing skies mid-day Friday. Snow surfaces may quickly become wet and weak on steep solar aspects. If you see trees shedding snow, or rollerballs and pinwheels, expect wet loose avalanches to follow. Although these avalanches may be small, they could knock you off your feet and carry you into trees, rocks, cliffs, or other obstacles. They may even trigger slab avalanches as they run downslope. Watch for changing conditions throughout the day, and move to shaded or lower angled terrain to avoid the problem. 

    (1/23/2021) Example photo of loose wet avalanches in steep, rocky, sun-exposed terrain.

Avalanche Discussion

The 8-12in inches of snow we’ve received since Sunday is a welcome addition to our firm preexisting snowpack (observation). Strong and shifting winds accompanied this incremental load of cold, low-density snow creating variable loading patterns. Natural and triggered avalanches to destructive size 2 were reported recently in the adjacent West North Zone. Avalanches occurred on upper elevation, wind-loaded slopes breaking  6-24in deep on the slick underlying crust, as well as within new and wind drifted snow.

Carefully assess the snowpack as you travel, especially on the northern half of the compass where you might find layers of weak faceted snow associated with two prominent crusts buried 1-2ft by recent and windblown snow. These layers were the culprit in a couple of recent avalanches in adjacent zones, including one remotely triggered by a skier (observation). Shooting cracks and collapses were also observed, along with sudden and propagating fractures in snowpack tests (observation). There is uncertainty regarding the distribution and sensitivity of these buried weak layers. Evidence exists but is not always easy to find. Weak snow could be above and below the crusts, or not present at all. The variability may be the biggest challenge, so investigate each slope you plan to ride individually, as what you find in one area may be different from the next.

The new snow is improving riding conditions following a period of cold, dry weather January 17-24, but firm and icy conditions still linger. At low elevations, the snowpack is still thin, with plenty of non-avalanche hazards present like open creeks, downed trees, and icy trails. 

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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