Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

Wed
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

The snowpack has not yet adjusted to the large amount of snow produced during the storm, maintaining dangerous avalanche conditions on Tuesday. Avalanches may be large enough to injure, bury, or kill you. Cautious route-finding and conservative decision-making are essential.

Problemi valanghivi

  • Storm Slabs

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

    We have had almost continuous, and often heavy, precipitation since 12/29, producing anywhere from 3-5 feet of new snow around Snoqualmie Pass and several potential weak layers in the upper snowpack. On Tuesday, Storm Slab likelihood will increase as you ascend in elevation and on wind-loaded slopes. Slabs may involve new snow or break several feet deep into the storm and wind-loaded snow from the past week. Slabs that start small could also entrain significant amounts of snow resulting in large avalanches. Check for strong snow over weak snow, storm density changes, and bonding to the old snow surface as points of failure for Storm Slabs. Using hand pits and test slopes can give you good information, but may not clearly identify deeper layers of concern. When in doubt, default to terrain less than 35 degrees and allow the snowpack time to gain strength. 

    (11/25/2020) Test slopes can give you a lot of good information about how snow has set-up after or during a storm. This test slope shows that storm slabs are sensitive and propagating easily.

Avalanche Discussion

With around 10.5 inches of water since 12/29, this storm cycle certainly has produced for Snoqualmie Pass. Lower elevations finally got the snow they’ve been looking for, mixed with a bit of rain, minimizing the hazard slightly going forward. At middle and upper elevations, multiple feet of cold and dry snow sit atop a crust (1/1) that was formed by a brief warmup on New Year's Day. This crust may be difficult to find in some locations but may present itself to you when performing stability tests since we believe there to be some weak snow sitting just above it. Below the 1/1, you will again find multiple feet of mostly cold and dry snow sitting atop the 12/21 crust.

On Tuesday, we expect the bulk of avalanche activity to occur above the 1/1 where there are multiple potential weak layers. However, the threat remains for deeper layers below the 1/1 to fail, creating very large and deadly avalanches. We wouldn’t be surprised to hear of some isolated D3 avalanches occurring over the next few days. Natural avalanche activity should be trending downward on Tuesday, but still possible, while human triggered avalanches continue to be a major concern. Additionally, observations from the highest elevations have been extremely limited due to the ferocity of the storm cycle, giving us a fair bit of uncertainty. If the middle and lower elevations are any indication, we have had plenty of avalanche activity up there and suspect that to continue on Tuesday where conditions are ripe for possibly creating the largest and most destructive avalanches.

With cooling temperatures and some new snow, Loose Dry avalanches should also be on your radar on Tuesday. The slides can entrain snow and even trigger slabs as they run downhill. Don’t get swept off your feet by one of these slides in consequential terrain. Lasty, due to the significant storm totals in the past week, deep snow alone can be dangerous. Make sure to travel with a partner and to be aware of the danger. You can learn more at www.deepsnowsafety.org.

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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