Avalanche forecast

West Slopes Central

Northwest Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Dangerous avalanche conditions Sunday will require a conservative mindset. Anticipate rising hazard throughout the day as additional loading from new snow and wind increase the size, depth, and likelihood of avalanches. Avoid wind loaded slopes 35 degrees and steeper, and use caution as the icy crust underlying recent snow remains a good sliding surface for avalanches. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    The West Central Zone looks to receive another 4-8in of new snow over the next 24 hours. Triggering an avalanche large enough to bury, injure, or kill a person will be likely on upper elevation, wind-loaded slopes 35 degrees and steeper. Previously formed wind slabs still need time to stabilize, and fresh slabs will grow in size and distribution with new snow and wind.  

    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 slick and variable surfaces, and even weak, sugary snow in isolated areas. Look for obvious signs of instability like recent avalanches, shooting cracks, and collapses, and dial back your terrain choices if any of these red flags are present. Carefully assess how new snow has bonded to old snow surfaces as you travel using hand pits and small test slopes. Seek out lower angled and wind-sheltered terrain to reduce your risk.

    (1/29/2021) A human triggered avalanche (D2) in Mazama Bowl on a north aspect at 5600ft. The avalanche broke up to 2ft deep on a slick underlying crust, 40ft wide, and ran 600 vertical feet. (West North Zone)

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Rising freezing levels and the potential for rain on snow will cause concern for loose wet avalanches Sunday. 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 lower angled terrain to avoid the problem. 

    (1/1/2021) Example photo of rollerballs and pinwheels.

Avalanche Discussion

The 12-16in of snow we’ve received over the past week 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 prominent crusts buried 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. 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.

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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