Lawinenlagebericht

West Slopes Central

Northwest Avalanche Center
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Lawinengefahr

Fri
Hochgebirge
3 · Erheblich
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Veraltet — dieser Lagebericht ist 6 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

You could trigger a surprisingly large avalanche on a persistent weak layer that is now buried more than 3 feet deep. They are getting more difficult to trigger, but if you do trigger one the results will be catastrophic and you will most likely die. Stay off and away from large, open slopes that are greater than 35 degrees at higher elevations while this continues to be a problem.    

Lawinenprobleme

  • Deep Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3

    A persistent layer buried 3 - 5 feet down could fail with a human trigger. Sadly, a snowbiker caused 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. You can also see the short video about it in the media gallery below. Avalanches failed on this layer in many of the forecast zones in the last 2 weeks, and a number of them involved 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 could affect. Infrequent natural avalanches on this layer continue to surprise people at Snoqualmie Pass, and our conditions are very similar to theirs. 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 it 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 cornice drop in the West South zone on Saturday. It propagated widely and is believed to have run on the Mid-January crust/facet combo. It is not unlike what we are seeing here in the West Central zone. [E aspect, 6300'. Photo: Jeremy Allyn]

Avalanche Discussion

New snow instabilities have mostly healed by now. Keep in mind that if you were to cause a small avalanche, even a loose dry one, or if a cornice were to fail, that may add enough weight to trigger the deep slab. For this reason, continue to travel very cautiously in areas where the problem may linger, above approximately 4500ft.  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.  

The weakness 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 lost strength 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 happened 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 11 days (16 in total). Heading out on a suspect 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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