Bollettino valanghe

East Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 2 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

A slab of recent snow overlays a weak layer in the snowpack. Clear signs of instability are shooting cracks, collapsing, and recent slab avalanches. If you encounter any of these, stay off slopes steeper than 30 degrees.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–1.5

    There is a cohesive slab overlaying a weak layer of buried surface hoar at upper elevations. As you drop to middle elevations, the slab begins to lose cohesion, but the buried surface hoar remains. For this reason, triggering an avalanche is likely at upper elevations and possible at middle elevations. This weak layer is buried roughly 1 foot deep in most locations but could be found deeper in previously wind-loaded spots.

    Unlike some persistent slab problems where you can dig a snowpit and easily assess for poor snowpack structure (harder over softer snow), in this instance you will only be looking for a thin grey line of buried surface hoar which can be difficult to identify. Look for clearer signs of instability such as cracks shooting from your skis or machine, whumpfing, and recent slab avalanches. The best way to manage this problem while we wait for the snowpack to adjust to its new load is to avoid avalanche terrain. 

    (1/3/2025)

    Large shooting cracks triggered by a skier in the East South zone.

    Photo: Northwest Avalanche Center

Avalanche Discussion

We have confirmed that this layer of surface hoar we've been watching out for was buried on New Year's. It now has enough of a slab over it to collapse and cause an avalanche. We received reports of touchy conditions and triggered avalanches on this layer in the Ahtanum on Friday. Just over the border in the West South zone, another small avalanche was triggered on the same day with similar snowpack conditions. Persistent slab problems are tricky to manage so you're best travel practice will be avoidance while we gather more info and wait for the weak layer to heal.

At lower elevations, the slab overlays a robust crust which could act as a slick sliding surface. At the moment, we don't have much information regarding whether or not this is the case. So far, it seems like the slab currently lacks the cohesion to avalanche on top. But if you are moving around lower elevations and are finding signs of instability, mark this as a time to avoid steep slopes at all elevations.

In areas that have seen previous wind loading, an unstable slab will behave similarly to a wind slab avalanche. If you encounter hard snow surfaces, rapid changes in snow depth, and cornices, presume that deeper slabs of recently wind-drifted snow can be found just below ridgelines and in cross-loaded gullies. You will encounter the same signs: cracking, collapsing, and recent avalanches.

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