Boletín de aludes

West Slopes Central

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

You can trigger surprisingly large avalanches on steep slopes on Wednesday. New snow instabilities could fail up to 2 feet deep, while a lingering concern of avalanches in a weak layer buried over 3 feet deep are still a problem. Steer clear of slopes steeper than 35 degrees while these avalanche concerns continue. 

Problemas de aludes

  • Storm Slabs

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

    Storm slab avalanches can occur in the top 2 feet of snow which we received over the weekend. Although shallower than the deep persistent slab problem, these still could bury, injure or kill you. They may also step down to the underlying weak layer, creating an even larger avalanche.  

    This problem may present in different ways, with wind possibly creating slab qualities in the snow at higher elevations.  At lower elevations and non-wind affected areas storm slabs or loose dry avalanches are more of a concern. With this myriad of problems, avoid slopes steeper than 35 degrees at this time.

    (2/4/2021) This thin avalanche failed just above the 2/1 crust layer in the Snoqualmie Pass area. Similar natural and human triggered slides were reported by several nearby professionals. Photo Renne Shapiro.

  • Deep Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2–3

    A persistent layer buried 3- 5 feet down could fail with a human trigger. Sadly, a snowbiker triggered an avalanche on this layer in the East Central zone on Monday, and was buried and killed. The Accident Reports page provides more details about the incident. Avalanches failed on this layer in many of the forecast zones in the last 2 weeks, with a number of them alarmingly involving people. The layer is progressively more difficult to trigger as it gets buried deeper and more time passes. Take a look at the video in the media strip to give you an idea of the depth and reactivity of the problem, which is similar to what we’re seeing in this zone.    

    At the depth this layer is buried, it is unclear whether the sole weight of a person would trigger an avalanche unless they found a shallower spot, which is possible. It is well within the depth that a snowmobile would affect. For this problem, there are no obvious signs of instability like you might find with other avalanche problems. You need to dig down to the Jan 13 crust and make note of the layer above it, observing the presence of persistent grains and how readily that layer fails. I wouldn’t place all my bets on one pit for this sort of problem. The game is too dangerous to play the odds on. Broad open slopes and large features in areas steeper than 35 degrees is where you are most likely to find the weakness, so avoid those slopes at this time. 

    (2/6/2021) This slab was intentionally triggered by a small cornice drop on Saturday. It propagated widely and is believed to have run on the Mid-January crust/facet combo. [E aspect, 6300'. Photo: Jeremy Allyn]

Avalanche Discussion

Avalanche problems related to new snow and wind are concerning enough, but the lingering deep slab instability poses a risk with even more uncertainty and higher consequences. A conservative mindset is crucial for getting through this period unscathed. Right now finding those lower angle areas or traveling through tighter trees are your ticket to surviving this rough period with the snowpack.  

Instabilities began after the atmospheric river event ended with a stout crust forming (Jan 13). Only a few inches of snow followed over the next 11 days, which weakened as it sat exposed to the sky. Snow began to fall Jan 24, and since then we have continued to see avalanches occurring on that Jan 24 interface. An extensive avalanche cycle occurred Jan 30- Feb 2 after a more intense period of snowfall, and several close calls occurred in neighboring zones in the following days as backcountry users got out again. 

Our snowpack has some similarities with other weak snowpacks nationwide, where avalanche fatalities unfortunately had a remarkable presence in the last 10 days (16 in total). Heading out onto a steep slope for any reason is not worth the consequence of not making it home that night. Have this in mind while you travel in the backcountry during this period of unstable snow conditions.

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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