Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Mon
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Fresh snow and winds will increase the likelihood of triggering small avalanches in wind-drifted snow. Steer around steep terrain with fresh drifts. Very large avalanches on deeper weak layers are still possible. So, don't take unnecessary risks with this high consequence problem and avoid traveling on steep northerly aspects where this poor snowpack structure exists. 

Problemi valanghivi

  • Wind Slabs

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

    Fresh snow and moderate winds could form sensitive wind slabs along ridgelines and exposed terrain, particularly in steep, confined features. Visual clues, such as actively blowing snow, textured surfaces, and cornice formations, can help identify wind-loaded terrain. We expect these avalanches to be small, but even a small avalanche could have significant consequences in steep, rocky terrain. Steer around steep slopes if you see actively blowing snow or signs of instability such as cracks that shoot out from your equipment. 

    There is a chance that a smaller wind slab could step down to more deeply buried weak layers, becoming a very large and dangerous avalanche. 

    (11/26/2024)

    Shooting cracks in wind-drifted snow. 7,200ft, W. West fork of Cedar ck

    Photo: Will Govus

  • Persistent Slabs

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

    The only way to manage this problem is to avoid steep slopes on northerly aspects at mid and upper elevations. Avalanches may be easier to trigger near exposed rocks or wind-loaded slopes. Persistent problems take significant time to gain strength and small inputs, like the incoming storm, can disproportionately affect the weak layers' reactivity. While the likelihood of triggering one of these avalanches slowly wanes with time, the extreme consequences remain. These avalanches could break across entire slopes, run long distances, and even reach valley bottoms. A heavy snowmobile or cornice fall may make avalanches easier to trigger, but don't discount the potential for a person to hit the perfect, wrong trigger point on a slope. With our variable, complex snowpack, avoid tempting fate and choose low angle terrain or other aspects for backcountry travel.

    Multiple very large and widely propagating avalanches occurred in late February through the first few days of March. In two separate involvements near Harts Pass, riders were buried and in one incident, one person was killed. 

    Further west of Washington Pass, this layer is buried deeper and thick melt-freeze crusts exist in the overlaying snowpack, so persistent slabs may be less likely.

    (2/28/2025)

    A large avalanche near Hart's Pass that caught 2 snowmobilers and resulted in one fatality on February 28th. 

    HS-AM-D2.5-R4-O. Cone Mtn, NE, 6,800ft

    Photo: NCH

Avalanche Discussion

The storm system will move further inland on Sunday, bringing moderate to strong winds and snow. We expect the bulk of the precipitation to impact the region in the afternoon hours, but if snow begins earlier than forecasted, expect an increasing likelihood of small storm and wind slabs. While temperatures will slowly cool, a poor overnight refreeze might result in small wet loose avalanches or even cause wet avalanches on more northerly terrain that still holds cold, dry snow. 

On Sunday 3/2, NWAC Forecasters visited the site of the avalanche fatality near Harts Pass that occurred on 2/28. You can read the initial observation here. The final report will be issued in the next few weeks. In addition to this avalanche, forecasters found widespread persistent slab, wet loose, and wet slab avalanches in size up to at least D3.

While the January Drought Layer has been in our snowpack for over a month, with the lack of an overlaying slab there was only isolated activity in specific terrain on this weak layer. The late February storm brought 18" of snow, strong winds, and warmer temperatures, which formed widespread cohesive slab over the JDL for the first time since it was buried in early February. This resulted in a widespread natural avalanche cycle, with crowns up to a mile wide on steep northern terrain at upper elevations. The JDL is buried 2–3 ft (70-100cm) below the surface in the Washington Pass and Harts Pass areas, and ~4' deep for areas further west. An NWAC observer in the Hart's Pass area observed old crowns that failed on the JDL. Snow profiles around 6000ft showed some rounding of the JDL facets and snowpack test results were inconsistent. Despite unremarkable test results, given this weak layer's uncertain, variable, and tricky distribution it's best to settle into an entrenchment mindset until we have significantly more information or another significant loading event to test the JDL's reactivity. 

While persistent slab avalanches have been the focus since the late February storm, the warm weather that followed into the first days of March also brought down impressive wet avalanches, some up to size D3 (very large). Natural wet slides occurred as recently as Sunday near Harts Pass, including one that broke trees and gouged to the ground (SW, 4500ft). 

You can help us gather more data by submitting an observation HERE or via the Avy App. 

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