Boletín de aludes

Snoqualmie Pass

Northwest Avalanche Center
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Peligro de aludes

Mon
Alta montaña
4 · Fuerte
Límite del bosque
4 · Fuerte
Bajo el límite
3 · Notable
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Desactualizado: este boletín caducó 6 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Updated 6:43am: Increased danger rating to High due to higher snow totals than originally expected. Travel in avalanche terrain is not recommended.

If you head into the mountains on Sunday, uncertainty around the amount of new snow and dangerous weak layers in the snowpack should steer you away from slopes steeper than 30 degrees. Avalanches will occur and have the potential to become large and deadly.

Problemas de aludes

  • Storm Slabs

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

    Observations from Saturday are limited, but at least a few natural avalanches were observed by professionals before the storm really ramped up on Saturday afternoon. Winds were actively moving new snow into slabs on leeward slopes and the base of cliffs, while heavier snow fell over lighter snow as temperatures warmed, creating slabs. Precipitation should continue Saturday night into Sunday as freezing levels lower and strong winds persist, building slabs. These slabs may be larger and more reactive as you ascend in elevation or in locations where the wind has aided in their development. Look for multiple density breaks in the storm snow due to fluctuating freezing levels, wind, and different periods of precipitation intensity. You can use hand-pits, test slopes, or up-slope tests to check these density breaks for potential points of failure, or to see how the recent storm snow is reacting to your weight. This won’t tell you the whole story, though. You will need to dig to see how these slabs are affecting those deeper persistent weak layers. If you find instabilities during your testing or notice fresh/recent avalanches, avoid terrain 30 degrees and steeper.

    (2/6/2021) Multiple persistent weak layers were confirmed at the upper end of the NTL on Saturday (2/6). These layers are starting to get buried deeply by storm and wind slabs which have their own points of failure.

  • Persistent Slabs

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

    On Saturday, NWAC members were able to confirm that our two layers of concern at Snoqualmie Pass still contain weak snow above/below them. As storms continue to impact the pass, these layers are getting buried deeper in the snowpack, making any potential avalanche involving them large and potentially deadly. Triggering a smaller storm slab or wind-affected pocket in the upper snowpack could cause the snow to step down to these weak layers, creating destructive avalanches. Digging down to identify the weak snowpack structure in the area you are traveling can help you identify the potential for Persistent Slabs. But if you don’t find weak snow grains, don’t immediately rule these slabs out. Continue to gather more information and ease into terrain slowly. 

    (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

Updated 6:43am: We now expect naturals to be more likely than originally thought. Avoid avalanche terrain while this storm runs its course.

We do not expect a widespread natural avalanche cycle on Sunday, which has allowed us to drop the hazard to Considerable. However, there is some uncertainty around a convergence zone setting up, weak grains in the snowpack, recent avalanches, strong winds, and recent significant snowfall. These all point toward unstable conditions at Snoqualmie Pass and are enough to have us on edge. Do not be surprised if you come across some natural avalanches on Sunday, particularly during periods of intense precipitation. Human triggered avalanches are likely to occur. If convergence does set up over the zone, there could be longer or more frequent periods of intense precipitation, potentially driving higher avalanche danger.

The weak layers in the snowpack have been well tested the past few days, but due to the storm, observations have been limited and we cannot relay confidently what happened out there. All we can say for sure is that these weak layers continue to be positively identified by professionals throughout the zone and that they can create unpredictable avalanches that break in surprising ways. On Thursday, widespread small natural avalanches occurred at Snoqualmie Pass on the 2/1 crust. The Mid-January (1/13) crust/facet combo has yet to have any confirmed avalanches on it at Snoqualmie Pass but has been the culprit for multiple large avalanches throughout the Cascades over the past week. On Friday, Alpental Pro Patrol triggered a large avalanche on what is suspected to be the Mid-January crust in non-skier compacted terrain. This avalanche reportedly broke more widely and ran further than it has in close to a decade. All of this information should lead you to approach the mountains with caution if you choose to head out on Sunday. Do not get lulled into your standard method of approaching Snoqualmie Pass storms, and dial back your terrain choices from what you may normally pursue at Considerable danger. If you do head out, be conservative 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.

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