Bollettino valanghe

West Slopes South

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

The weather you experience will determine where to focus your attention. In cloudy or shaded areas use caution around wind-affected snow. On sunny slopes, expect natural loose wet slides. Either of these could serve as the trigger for much larger and scarier deep slab avalanches in big terrain.

Problemi valanghivi

  • Wind Slabs

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

    You may find shallow pockets of wind drifted snow, especially at mid and upper elevations on Monday. These thin slabs shouldn’t be enough to harm you on their own, but if they push you over a cliff or into rocks that could change. In bigger terrain, they could even serve as the trigger needed for a deep persistent slab. Cornices, drifts, and textured snow surfaces can help you anticipate wind-loaded slopes. Use caution below cornices, near rocks, and in confined chutes where these potential avalanches may trigger more easily.

    (3/7/2021) We intentionally triggered this small wind slab on a test slope near treeline. Small features like this can help highlight conditions on larger slopes. NW, 6100'. SS-ASc-D1-R2-S

  • Loose Wet

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

    The soft new snow sits over a frim crust. If the sun comes out on Monday, expect some of this snow to fall down. Watch for snow shedding from trees and rocks first. Next, you may notice new rollerballs. When you see these clues, think loose wet avalanches. Steer around similar slopes and seek out more shaded terrain. These slides may grow larger in areas where more than 6-8” of snow sits above the most recent crust.

    (1/23/2021) Example: Loose avalanche on steep sunny slopes from earlier this winter. Photo: Susie Glass

  • Deep Persistent Slabs

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

    Plenty of uncertainty continues to surround the deep persistent slab problem. A lack of recent avalanches gives us some hope, but don’t mistake this for signs of stability. Recent snow profiles continue to find the mid-January layer intact in some areas. Let the potential consequences of this problem shape your terrain choices. Any slide on this layer would grow very large, destructive, and deadly. Talk about these facts before engaging with larger avalanche paths. Limit your time in and near these potential giants. This includes not lingering in areas where slides may run or stop even well below treeline.

    (2/28/2021) This slide on Norse Peak was measured to be over 1000' wide and approximately 6 feet deep. It broke trees and is suspected to have run on Friday (2/27)

Avalanche Discussion

You may encounter very different weather conditions depending on where you travel in the West South zone Monday. Some locations may experience more sunshine than others. This could also change quickly over the course of the day. In cloudy areas or on shaded aspects, focus on the recent snow and how the wind affected it. On sunnier aspects, anticipate how the sun will change and potentially weaken the surface. Either of these small avalanches could serve as a trigger for deep slab avalanches. 

The West South picked-up 3-8” of snow this weekend. This new snow sits above a strengthening crust (3/5)  in many areas and adds to a generally strong and well settled upper snowpack. Windy weather on Sunday reshaped the surface in some regions creating deep drifts and scoured slopes. You may still find several of our recent interfaces and crusts in snow profiles. However, the primary layer of concern remains the mid-January interface. This facet-crust combination rests 6-11’ below the snow surface. Snow profiles and avalanches over the past week continue to feed the immense uncertainty surrounding this persistent weak layer. Very large avalanches near Crystal and one near White Pass occurred between 2/26 and 3/4. Several of these slides broke large trees and traveled to the bottom of their runout zones. Even as we slowly gain some confidence in the snowpack with cooler weather, this low-likelihood/high-consequence issue continues to shape our terrain and travel 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.

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