Lawinenlagebericht

East Slopes South

Northwest Avalanche Center
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Lawinengefahr

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

While we are a few days out from the storm, weak snow lingers beneath the recent storm snow. You may still trigger avalanches on this weak snow buried 1-2ft deep. Be particularly suspicious of steep terrain with sparse trees and vegetation. You should approach new terrain cautiously and use small, inconsequential test slopes to see how the snow reacts. If you see shooting cracks, feel the snowpack collapse, or the test slope produces a mini avalanche, you should stick to lower angle terrain. 

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1.5–2.5

    Large avalanches have run on recently buried surface hoar or deeper weak, sugary facets from Mid-November in all the zones surrounding East South. During avalanche mitigation efforts, Crystal Mountain and Mission Ridge produced avalanches that ran near the ground on the Mid-November facets. We suspect a skier triggered avalanche near White Pass ran on recently buried surface hoar (12/8). We have limited direct observations from the East South zone. However, even without direct observations, it's highly likely that similar snowpack and avalanche conditions exist in East South. These avalanche problems take longer to strengthen and heal than a typical storm snow problem. We have significant uncertainty about the distribution and reactivity of these weak layers, so assessing the snowpack is essential before committing to steep slopes. 

    Approach new terrain slowly and assess conditions as you ascend in elevation. Steep, northerly aspects are the most suspect location for these deeply buried weak layers to exist. Be particularly suspect of sparsely vegetated slopes, steep open terrain below ridges, steep rolls in the middle of slopes, and near rocks or cliffs where you are more likely to trigger these avalanches. Dig down and identify sugary, faceted layers or feathery surface hoar layers buried in the snowpack. You can also use small test slopes to see if you can get a slab of snow to move. Stay on lower angle slopes if you find the overlaying snow slides easily on these layers, experience whumping collapses, or observe cracks shooting out from your equipment. 

    (12/10/2022)

    A distant view of the skier-triggered avalanche at White Pass on 12/10. This slide is suspected to have failed on buried surface hoar. 

    Photo: Paul Przybylowicz

Avalanche Discussion

Recent observations near White Pass and Crystal Mountain have identified and shown unstable snowpack test results on the surface hoar buried 1-2ft deep below the recent storm snow. While we have limited direct observations from the East South zone, avalanches on this layer are widespread enough to impact the East South Zone. I was out in Ahantum Meadows earlier in December and found weak faceted snow close to the ground. Last weekend, avalanches at Crystal Mountain ran on this deeply buried, sugary snow layer. Avalanches involving weak persistent snow layers are tricky and tend to stick around for a while. The snowpack will seem to adjust over time to a new snow load, then another storm rolls into the mountains, and we see avalanches breaking down onto these older layers again. Someone hitting a shallow spot near rocks or cliffs also can trigger these avalanches or large triggers such as explosives during avalanche control work. This uncertainty should make you take a step back and closely evaluate slopes that may harbor this weak snow.  

The sun has been warming southern aspects, and now most sun exposed terrain has a melt freeze crust on the surface. Another sunny day is in the forecast for Tuesday, with slightly warmer temperatures. Snow on steep, southern aspects may get heavy and wet. You could see roller balls or wet snow sliding off steep terrain near rocks or cliffs. Stay out from under cliffs or rock faces that begin to shed snow. 

If you get out into the East-South Zone, tell us what you see by submitting an observation on our public observation platform!

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