Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Pay attention to the weather and think about how it may impact the snow. Changes in the sky cover will drive the type of avalanche issues you may encounter. Choose terrain where you can easily identify and avoid avalanche slopes in order to adapt to the changing conditions.

Problemi valanghivi

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1

    The recent snow from this weekend sits atop a firm crust at the Pass. If you experience periods of sunshine on Monday, expect some of this snow to slide downhill. The snow shedding from trees and rocks may serve as your first clue. Next watch for new rollerballs on very steep slopes. When you see these signs, the snow surface is primed for loose wet slides. Steer around similar areas and seek out shadier terrain. Any of these avalanches may run quickly or far over the recent crust.

    (2/28/2021) Example: New rollerballs on a sunny slope earlier this winter.

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1

    Travelers observed shallow wind slabs at Snoqualmie Pass on Sunday, along with significant wind loading. You may still trigger these potential avalanches on the lee sides of ridges or exposed features. Cornices, drifts, and textured snow surfaces can help you anticipate wind-loaded areas. Even though these slides should remain small, they can harm you if they push you over a cliff or into rocks. They may even serve as the large trigger needed for a deep persistent slab in bigger terrain. Pay attention and use caution below cornices, on rocky slopes, in confined features where these avalanches may trigger more easily.

    (3/7/2021) Textured snow surfaces like this can help you anticipate which slopes or features could harbor wind slabs. Photo: Ian Nicholson

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    3

    The last known deep slab avalanche occurred at Snoqualmie Pass a week ago. While the lack of activity gives us some hope, don’t mistake it for stability. Recent snow profiles at the Pass show the weak snowpack structure remains largely unchanged. We reentered the classic low-likelihood/ high-consequence scenario. Before engaging with very large avalanche paths, have a frank discussion about the consequences of these avalanches. Any slide would result in a very large, destructive, and unsurvivable event. Limit your time in these bigger avalanche paths, including areas down in the trees where slide may run or stop.

    (3/1/2021) A very wide, very deep avalanche released from the east bowl of Chair Peak at some point between Sunday night and Monday morning (NE-E-SE 5800; HS-N-D3.5-R4-O). Photo: Bryce Hill

Avalanche Discussion

Monday’s forecast depends a lot on the weather you experience, and spring forecasting can be tricky. Part of the zone could see snow showers while other areas bask in the sun. Let the weather you encounter help determine where to put your attention. Under cloudy skies and on shaded aspects, focus on the new snow problems like wind slabs. On sunnier slopes, watch for loose avalanche issues. Either of these slides could trigger the much larger and scarier deep persistent layer. 

The Pass received 6-8” of snow this weekend that generally bonded well to a strengthening crust (3/5). In exposed terrain, the winds reshaped the snow surface forming deep drifts and scoured slopes. This adds to a generally strong and well-settled upper snowpack. While several recent crusts remain visible, the mid-January interface continues to serve as the primary layer of concern. This facet-crust combination sits 8-10’ below the snow surface in most locations. Numerous avalanche cycles occurred on this layer over the past few weeks. The most recent slides broke trees and descend to the valley bottoms. While we slowly gain confidence in the snowpack, the immense uncertainty surrounding this layer continues to shape our terrain choices. 

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