Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Don’t ignore the large amount of precipitation we just received. The snowpack needs time to heal and may not heal as quickly as you are used to. Dial back your terrain choices as we navigate uncertainty about deeper weak layers.

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    The Pass overproduced on its water numbers on Saturday night and Sunday, resulting in a bit more snow than we had anticipated. We are not done yet, as moderate snow showers are set to continue into Sunday evening. With so much recent snow coming in different pulses and with strong winds, there are multiple density breaks and interstorm layers that are capable of failing in the upper snowpack. Much of the snow that fell Saturday night through Sunday is low-density, so you could find that loose avalanches are more of a problem in some areas where slabs haven’t developed. Below that low-density snow could be more upside-down snow due to heavy wet snow falling on top of lighter snow earlier in the weekend. Take some time to look at all of the recent storm snow on Monday to see 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 where you are traveling. Look for shooting cracks, textured snow surfaces, or smooth pillow-like piles of snow while you travel to identify those wind-affected areas. Avalanches will be easier to trigger near rocky terrain like the base of cliffs or gullies, on convex features, wind-affected terrain, or steep slopes that are greater than 35 degrees.

    (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. [Photo: Alpental Pro Patrol]

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    Two layers of concern are getting buried deeper throughout the Snoqualmie Pass zone. The Mid-January crust/facet combo (1/13) contains weak snow grains that have been reactive in tests by professionals and have been the culprit of large to very large avalanches for the past week in adjacent zones. This layer is suspected to have been the point of failure for a large slide triggered by Alpental Pro Patrol on Friday and will be buried over 3 feet deep in many locations. The 2/1 interface is generally around 30cm above the Mid-January crust, may contain weak grains above and below it, and is a bit more subtle in some areas of the zone. This interface was extremely reactive on Thursday and still showed signs of life in pit tests over the weekend.

    You can dig down to determine the existence of these weak layers, but a single hole in the ground shouldn’t be a tool for ruling them out in your area. Continue to approach terrain over 30 degrees with caution. These slides can propagate widely and be triggered from far distances away. We have uncertainty about what it would take to trigger one of these avalanches right now, but if you trigger a large enough storm instability, the avalanche could step down and trigger these layers. If you are caught in one of these avalanches at this point, it may be unsurvivable.

    (2/5/2021) This slab was triggered by a single explosive on Friday (2/5) by Alpental Pro Patrol. The explosive dropped a cornice onto the slope which propagated widely across the width of the terrain feature. The slide is suspected to have failed on the Mid-January crust/facet combo. [Photo: Alpental Pro Patrol/Mac Miller]

Avalanche Discussion

On Saturday, a very large avalanche on the eastern border of the Snoqualmie Zone resulted in a full burial. Luckily, this person was recovered by their partners and unharmed. It seems as if the avalanche broke in a way that is consistent with other avalanches we have confirmed on persistent weak layers throughout the region. All of the recent snow has definitely tested these layers and we are starting to see some more consistent results on them within our zone. On Sunday, reports of whumpfing in the zone indicate that the snowpack is unstable. Additionally, Alpental Pro Patrol triggered a slab during control work that was up to 5 feet deep and failed on the Mid-January crust/facet combo. They reported multiple 2-4 foot slabs in wind-loaded terrain near the base of cliffs and other rocky features, highlighting what we have been talking about the past few days with multiple potential points of failure. 

With the amount of snow we just received, the hazard rating would be Considerable on Monday even without the existence of these potential deeper instabilities, and we would likely be hearing about plenty of avalanches by Monday night, just like we are starting to hear about more avalanche from Sunday. The confirmed weak snowpack structure should have you choosing even more conservative terrain than you normally would as a storm winds down. If you do head out, use caution and let us know what you see by submitting a public observation.

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.

Regioni coperte