Boletín de aludes

Snoqualmie Pass

Northwest Avalanche Center
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Peligro de aludes

Thu
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

If you choose to travel in the mountains, dial back your terrain choices. High consequence slides are possible on weak layers deeply buried in the snowpack. Avoid steep slopes over 35 degrees where triggering an avalanche is more likely.

Problemas de aludes

  • Storm Slabs

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

    You will find plenty of low-density snow in the uppermost snowpack at Snoqualmie Pass in many locations. Below this cold light snow, you will find recent storm snow that has consolidated into a slab. In some areas, the slab will be on the surface, possibly due to wind effect. Depending on which setup is more prevalent in your area, you will be dealing with Storm Slab avalanches, Dry Loose avalanches, or both. Both avalanches are dangerous, especially when there is so much snow. Avalanches will be more likely near rocky terrain like the base of cliffs or gullies, on convex features, or steep slopes that are greater than 35 degrees. Use test slopes, hand pits, or uptrack tests to see if there is slab potential in the uppermost snowpack where you are traveling. If you find only light and fluffy snow, dig down and look at what’s under the low-density snow. Cold temperatures will keep the sun’s influence minimal, but some sun breaks could cause the snow to “slab up” or trigger Dry Loose avalanches.

    (2/8/2021) Both Dry Loose and Storm Slabs were triggered by skiers on Monday at Snoqualmie Pass. These problems will continue for a few more days.

  • Deep Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    3

    Our two buried weak layers can be found 120 and 150cm below the surface on average. At this point, it doesn’t matter which one of these layers fails initially, any avalanche will be so large that it will step down to the Mid-January crust around 150cm deep. You will not be able to see red-flag signs of instability as you travel to indicate danger due to the depth at which these layers are buried. You need to know that this setup is prevalent throughout the zone, has been the source of many recent incidents, and is not healing or going away anytime soon. Even if you believe the likelihood of triggering may be decreasing due to its burial depth, the consequences remain sky-high. The likelihood of these slides increases as you ascend in elevation but can still exist at lower elevations. We have some uncertainty about what it would take to trigger one of these slides at this point, but it could be a step down from another avalanche, a snowmobile, cornice, or even just a shallower spot in the snowpack. We believe that the most likely places for these slides to run are open terrain features and start zones over 30 degrees. 

    (2/8/2021) This avalanche failed on the Mid-January crust/facet combo and resulted in a fatality on Monday. [HS-AV-R3-D3-O]

Avalanche Discussion

Unfortunately, on Monday we received word of a fatality on the eastern border of the Snoqualmie Pass zone. Although technically this event occurred in the East Central, after reviewing the accident site, NWAC forecasters from both Snoqualmie Pass and East Central agreed that the snowpack in this area is currently more in line with conditions at Snoqualmie Pass. The snowpack structure was reported to be almost identical to that found in the Alpental Valley on Monday morning by NWAC forecasters and the crown depth was found to be 4-5 feet deep with the Mid-January crust as a bedsurface. This incident is the latest in a line of warnings that have had us on edge here at NWAC and we have been relaying to you in the forecast. On Friday, Alpental Pro Patrol notified us of unusual avalanche control results. They continued to receive active and unusual results throughout the weekend. Saturday, a public observation let us know of a full burial on the eastern border of our zone. Luckily no one was injured in this incident. On Sunday, a large avalanche incident occurred at Stevens Pass, which has a very similar snowpack structure to ours. 

All of that said, it’s deep out there right now at Snoqualmie Pass and the snowpack problems are complex and not what you may be used to managing. Do not ignore the large snow totals, relatively cold weather we are experiencing, or the persistent weak layers. The cold weather will not help the snowpack to heal as quickly as you may be used to, and persistent weak layers heal even more slowly than standard storm instabilities. Just the sheer volume of snow can be hazardous if you fall or get knocked off your feet by a relatively small avalanche. You can learn more about snow immersion hazard here.  Continue to approach terrain with caution and be safe out there.

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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