Boletín de aludes

Snoqualmie Pass

Northwest Avalanche Center
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Peligro de aludes

Wed
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

We just got a lot of snow in a relatively short period of time. Continue to give the snowpack time to adjust to its recent load by making conservative terrain choices on Tuesday. Weak layers in the snowpack are now buried deeply and are not going away anytime soon.

Problemas de aludes

  • Storm Slabs

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

    There is a lot of recent snow in the Snoqualmie Pass zone and it gets deeper as you ascend in elevation. This snow is the result of a series of storms that had different freezing levels, wind speeds, and even precipitation types. The storm parade finished cold, delivering light fluffy snow. This is what you will encounter near the surface, and could drive loose avalanche problems, particularly on steeper terrain features. As you dig deeper, you’ll find multiple interstorm layers, density breaks, and slabs to be concerned with. Take a look at which layers are reactive and how deep they are. You can use test slopes, hand pits, or uptrack tests to see if there is slab potential in the uppermost snowpack where you are traveling. You are going to have to dig to look at what layers are under the low-density snow. Avalanches will be more likely to be triggered near rocky terrain like the base of cliffs or gullies, on convex features, or steep slopes that are greater than 35 degrees.

    (2/8/2021) Both Dry Loose and Storm Slabs were triggered by skiers on Monday at Snoqualmie Pass, sometimes on the same slope. 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

    Observations from NWAC forecasters on Monday found the 2/1 interface to be 120cm deep and the Mid-January crust/facet combo to be 150-160cm deep. These weak layers are now deep enough in the snowpack that you will not be able to see red-flag signs of instability as you travel to indicate danger. Just because you are not seeing obvious signs of instability does not mean that you have chosen the appropriate terrain. The most likely places for these slides to run are large open terrain features over 30 degrees, with a higher likelihood as you ascend in elevation. 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 a Storm Slab avalanche, a snowmobile, cornice, or even just a shallower spot in the snowpack. What we do know is that if you trigger one of these avalanches and are caught, it would most likely be unsurvivable.

    (2/7/2021) This slab was triggered during control work by Alpental Patrol. Although it is in wind-loaded terrain, it failed on the Mid-January facet/crust combo and was up to 5 feet deep.

Avalanche Discussion

Preliminary avalanche incident information Monday February 8th, 2021: Two snow bike riders were caught and buried by a very large avalanche in the mountains west of Salmon la Sac Sno-Park along Cle Elum Lake. One snow biker was partially buried and was able to dig himself out. The other rider was fully buried and killed by the avalanche. The avalanche occurred on a north aspect at 4400 ft in the Knox Creek drainage. This terrain lies in NWAC’s East Central forecast zone. Avalanche classification: HS-AV-R3-D3-O. 

All of us at NWAC want to extend our condolences to family, friends and the local community following this tragic event.  

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It’s deep out there right now at Snoqualmie Pass. Do not ignore the large snow totals and relatively cold weather we are experiencing. 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. If you choose to travel in the mountains, make conservative terrain choices, being aware of the high consequence slides that are possible on those deeper layers. With so much snow, loose snow can have consequences if they’re able to knock you off your feet near small terrain traps, or even if you fall and are unable to get up. Learn more about snow immersion hazard here. 

A little bit of visibility on Monday gave us the ability to look around the Alpental Valley a bit. Large avalanches were observed to have run on Chair Peak with fresh debris down by Source Lake.  On Sunday, Alpental Pro Patrol reported a very active day with slabs as deep as 5 feet being triggered during control work. After receiving reports of a full burial on the eastern edge of our zone on Saturday, a large avalanche incident occurred on Sunday at Stevens Pass. This should be a free lesson to those traveling at Snoqualmie Pass since the snowpack setup between the two zones is similar right now. Please 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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