Bulletin d’avalanche

East Slopes Central

Northwest Avalanche Center
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Danger d’avalanche

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

Points saillants

A storm system will create new snow instabilities at the surface that should be easy to spot. Additionally, new snow could add enough weight to the snowpack that a big triggered avalanche failing in weak layers deeper down might happen. Signs of instability are cracks shooting out from your equipment, audible collapsing, and recent triggered or natural slab avalanches. Keep it simple on Sunday and let the snowpack adjust before jumping onto slopes steeper than 30 degrees.

Problèmes avalancheux

  • Storm Slabs

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

    This problem will be more apparent the further west and closer to the Cascade Crest you are in the zone. In complex and exposed terrain where the wind has transported snow, new slabs will be deeper and denser. Slabs will also be forming over older wind slabs in exposed terrain at middle and upper elevations on all aspects that could still be sensitive. Furthermore, a triggered avalanche in new/recent snow could break deeper and trigger a larger persistent slab avalanche in areas that harbor a weak snowpack. Look for red flag indications that storm and wind-affected snow is unstable, even in more eastern parts of the zone. Blowing snow and cornices are obvious clues that old and newly wind-affected snow exists. Hand shears and safe test slopes representative of what you hope to ski or sled are easy ways to check the bond between new and old snow.

    (12/26/2024)

    A storm slab triggered by explosives during morning mitigation efforts at the Summit at Snoqualmie earlier in the season.

    Photo: Summit at Snoqualmie Pro Patrol

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1.5–2

    The weak and variable snowpack throughout the zone may be put to the test again on Sunday. The forecasted storm totals could be enough to tip the scales - most likely closer to the Cascade Crest, where more snow will fall - or they could not. You might not want to be the test subject with uncertainty like this. Persistent slab avalanches can break in surprising ways and wider than expected. You can dig down and look for easily identifiable poor snowpack structure - harder snow over weak, sugary snow - but use the guidance laid out in the storm slab problem to select your terrain for the day while we wait to see how this problem reacts.

    (2/14/2025)

    You can clearly see the grey-ish line of weak facets in the wall behind the failed snowpack test. These weak grains aren't hiding, they're easy to spot. 

    Photo: Dallas Glass

Avalanche Discussion

With somewhat unimpressive storm totals and heavy wind slab messaging within the storm slab problem, you might wonder why a wind slab problem wasn't forecasted. The answer falls in the kind of snow that is being buried. Reports of surface hoar development came on Saturday for this zone and surrounding zones. Where there isn't surface hoar, there is probably still some low density snow that made the last week of skiing and riding so enjoyable. These snowpack conditions are enough to convince us that the new snow problem will be more widespread than just exposed, wind-affected areas. 

Since the onset of the persistent slab problem, the East Central zone has not seen a significant number of signs of instability. There have been no confirmed persistent slab avalanches up until this point. Although the January Drought Layer (JDL) was and still is pervasive, the problem lacked a cohesive and deep enough slab a lot of areas. Now, that slab will be considerably more settled and will be getting compressed by new snow. With just a few more inches of "seasonably dense" new snow, will this be when we see a more widespread avalanche cycle? Time will tell...

There is a small chance that precipitation will fall as rain at lower elevations, primarily in the morning on Sunday. If you find yourself getting rained on, expect to see wet loose avalanches. They will most likely be small, but a small avalanche can knock you off your feet and carry you over hazards such as rocks and cliffs. 

Although we aren't telling you that travel in avalanche terrain is not recommended, it should be clear by now that managing Sunday's avalanche hazard is complex. We do recommend that you keep your tour plan simple to have a more enjoyable day in the backcountry.

Submit an observation to help NWAC Forecasters reduce uncertainty. It can be short, simple, and even anonymous. Any information you have will help us write more accurate forecasts that will, in turn, better help guide your backcountry decision making.

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