Bulletin d’avalanche

East Slopes South

Northwest Avalanche Center
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Danger d’avalanche

Fri
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

There is still a possibility of triggering an avalanche on weak snow lingering beneath the recent storm snow. The most likely areas to find this unstable snow is at higher elevations on slopes with sparse trees and vegetation. Before committing to steep slopes, 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. 

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Stability around the recent storm snow interface (12/8) seems to be improving. However, there is still potential to trigger an avalanche on this layer. Unlike a typical storm snow interface, the new snow fell on weak, persistent grains that take a while to strengthen and heal. Over the weekend, reports came in with skier triggered avalanches on this layer, and Crystal Ski Patrol triggered an avalanche on a 3-4ft deep weak layer that was formed and buried in November. We have limited direct observations from the East South zone. However, similar snowpack and avalanche conditions likely exist in East South. 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. Weak layers buried by the recent storm may be more widespread. 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. 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. Morning valley clouds may burn off in the afternoon or not reach higher elevations. If you find yourself under blue skies, note that 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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