Bollettino valanghe

East Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Mon
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

A slab of new and recent snow overlays a weak layer in the snowpack. Stay off steep slopes if you encounter shooting cracks, collapsing, and recent slab avalanches. Wet snow avalanches will be a concern with rain and warm temperatures. Be suspicious of slopes steeper than 35 degrees if you're moving through heavy, mushy snow.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    A cohesive slab overlays 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 1-1.5 feet deep in most locations but could be found deeper in 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), you will only be looking for a thin grey line of buried surface hoar that will 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: Joe Dellaporta

  • Loose Wet

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

    Peak instability will be overnight on Saturday into Sunday when rain falls at lower elevations. However, freezing levels will rise to 4500 ft on Sunday so the already wetted snowpack will continue to see some instability. The typical progression of wet loose avalanches involves rollerballs and pinwheels that lead to point releases. They often start from cliff bands. Other signs that indicate warming are sticky snow surfaces, chunks of snow falling off trees, and water dripping from cliffs. If the snow under your skis or sled feels heavy and sticky, consider sticking to slopes less than 35 degrees.

    (12/31/2024)

    Lots of rollerballs that never quite turned into a wet loose avalanche in the East South zone.

    Photo: Payton Schiff

Avalanche Discussion

We have confirmed that this layer of surface hoar on the watch list was buried on New Year's. It now has enough of a slab on top to collapse and cause an avalanche. This slab will continue to grow with an additional 2-6 inches of new snow on Saturday night. Additionally, if it warms up enough in the afternoon, the slab could form more cohesiveness and have a higher likelihood of propagation.

An NWAC Forecaster experienced touchy conditions on the buried surface hoar layer in the Ahtanum on Friday. He also got reports of small triggered avalanches on the same day in the area. Just over the border on White Pass in the West South zone, another small avalanche was triggered on Friday 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.

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. The slab will be deeper and an avalanche will be more consequential. You will encounter the same signs: cracking, collapsing, and recent avalanches.

There is some uncertainty about how the rain will affect the likelihood of wet snow avalanches on Sunday. For starters, there is a discrepancy in the timing of some weather inputs on Sunday. Most weather models suggest that the snow and rain will mostly turn off by early morning, but others point towards continued precipitation into the daylight hours. Secondly, the robust crust found at lower elevations that may be under little new snow will have to break down first before it begins to lose strength. All in all, consider this: if you are out and still getting rained on or you are punching through the snowpack deep below the crust, anticipate a higher likelihood.

Help NWAC Forecasters reduce uncertainty by submitting an observation!

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