Lawinenlagebericht

East Slopes North

Northwest Avalanche Center
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Lawinengefahr

Tue
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

You could trigger an avalanche in shallow wind-drifted slabs. Steer around steep slopes in exposed terrain and below ridgelines with textured wind drifts. There is still potential to trigger a very large avalanche that breaks widely across terrain, considering the high consequences, just avoid steep northerly aspects where this problem lurks. 

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–1.5

    Fresh snow and moderate winds could form sensitive wind slabs on steep slopes below ridgelines and exposed terrain. Visual clues, such as actively blowing snow, textured surfaces, and cornice formations, can help identify wind-loaded terrain. Steer around steep slopes if you see actively blowing snow or signs of instability, such as cracks that shoot out from your equipment. You can also use small wind-affected test slopes to see how the snow reacts, snow that cracks and slides easily means you are likely to trigger a wind slab. We expect most avalanches to be small, but even a small avalanche could have significant consequences in steep, rocky terrain. As you climb in elevation, where more precipitation will fall as snow, avalanches could be larger. 

    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

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    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 therefore, diligent decision making and patient terrain management. 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 a person could just 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 was slow to move inland on Sunday, so we expect most of the moisture and winds to impact the area overnight. This storm will start warm, with rain at lower elevations, before cooling and bringing snow levels back to seasonal norms. So, as you climb in elevation, expect more fresh snow and larger avalanches. We don't expect these modest precipitation amounts to increase the likelihood of triggering a persistent slab. However, there is still uncertainty because sometimes small weather inputs can disproportionately affect the stability of these weak layers.

The cloud forecast for Monday is hard to pin down, but it seems there is a chance for the sun to break out in the morning after precipitation tapers off. But since it's Mid-March, snow on sunny slopes won't take long to turn into wet mush. With a slick crust underneath, wet avalanches could easily travel further than expected. Move to shady or lower angle terrain if you see rollerballs or natural wet loose avalanches.

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 that 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. Snow profiles between 6000-7000ft show some rounding and strengthening of the JDL, but overall the weak layer and slab characteristics have not changed significantly. Given this weak layer's uncertain, variable, and tricky distribution, it's best to settle into an entrenchment mindset until we see a more substantial change in the snowpack structure. 

NWAC Forecasters visited the site of the avalanche fatality near Harts Pass that occurred on 2/28. You can read the initial observation here. 

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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