Boletín de aludes

West Slopes South

Northwest Avalanche Center
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Peligro de aludes

Sat
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 5 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Recent very large avalanches, multiple days of warm weather, and increasing wind and precipitation are enough to maintain dangerous avalanche conditions on Friday. While you could find new piles of wind-drifted snow to steer-around, it's the deep avalanches that should have your attention and drive your decision-making.

Problemas de aludes

  • Deep Persistent Slabs

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

    The Mid-January crust that has been the culprit in some very large recent avalanches was found over 5 feet (173cm) below the surface of the snow near Crystal Mountain by NWAC team members on Thursday. This depth may vary across the zone, particularly on the volcanoes where it may be much deeper. The timing of these destructive avalanches is almost impossible to predict, but if they fail, they will be very large and being caught would almost certainly be fatal. The best way to mitigate your risk is to choose terrain that avoids large start zones, avalanche paths, and runout zones. These slides have been running long distances toward valley bottoms and approaching historical maximum runouts. Many areas we often consider as “safe” do not currently fit that description. 

    (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)

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1

    A bit of precipitation associated with some strong winds will impact the zone on Thursday night and Friday, with more precipitation forecasted for Paradise. Freezing levels will slowly lower throughout the forecast period and you could find that some shallow Wind Slabs have formed by day’s end on Friday. Slabs should be larger and potentially more reactive as you ascend in elevation, particularly above the rain/snow line. Look for these slabs on leeward slopes near ridgelines, near rocky features such as the base of cliffs or the sides of gullies, or mid-slope on steep features such as convex rollovers. If you notice textured snow surfaces or smooth pillow-like piles of snow, steer around those wind-loaded features. 

    (3/4/2021) These natural avalanches occurred in Union Creek in the Crystal Mountain backcountry and are suspected to have run between Monday (3/1) and Wednesday (3/3). [E aspect ~6500' Photo: Shane Robinson]

Avalanche Discussion

On Thursday, NWAC team members were able to dig down to the Mid-January crust on a similar aspect and elevation to many of the natural avalanches that occurred within the past week near Crystal Mountain. Although not a perfect comparison, we found the crust to be over 5 feet (173cm) down from the surface and that weak snow did still exist above and within the crust. We also found that the 2/11 layer still has some weak snow and this layer has recently been reactive at Crystal Mountain during control work measures. 

As we look toward the weekend, temperatures should remain elevated into Friday morning. The temperature, possibility of precipitation, confirmed poor snowpack structure, and recent avalanches on the Mid-January crust all point toward dangerous avalanche conditions and the potential for more Deep Slab avalanches. We have some uncertainty around what it would take to trigger one of these slabs at this time, but we believe that a large cornice fall could do the trick. The warm temperatures and some light rain will only further destabilize cornices and blocks of snow sitting on rocks and cliffs, increasing the possibility of them falling. Continue to be leery of slopes with cornices overhead. And look out if you’re on a ridgeline, cornices notoriously break further back than you expect them to. The light rain could also trigger a few lingering Wet Loose avalanches, particularly on slopes that haven’t seen direct sunshine recently. Remain vigilant with your terrain selection and let the consequences of the Deep Slabs guide you.

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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