Bollettino valanghe

East Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

Sat
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Dangerous conditions persist because people could trigger slabs 1.5-3ft deep that run on the ground.  Be especially careful to avoid steep open slopes at any elevation facing  Northwest to Northeast. This problem may stick around for a while, because the weak, sugary facets responsible for the instability are slow to heal. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1.5–2

    Heed signs of danger such as loud audible whumphs, shooting cracks, and pay attention to signs of recent avalanches as you travel. You could trigger wide avalanches 1.5-3ft deep on old layers of facets and crust near the ground. Be especially leery of large, steep slopes, and any areas with stiffer snow that may have been deposited by wind. Areas above 5,000ft that face NW-NE may be the most likely place to trigger this deeper weak layer. However, folks are finding signs of instability even as low as 3,600ft in old clear cuts on north aspects. 

    These can be triggered from below, on shallower angled slopes that are connected to steeper ones. Slides could run on the ground, increasing consequences of going for a ride. If you decide to enter steep, open terrain features on the north half of the compass, you're gambling with these dragons. 

    Example persistent slab avalanche from the Salmon la Sac drainage in 2021. Photo: Matt Primomo

Avalanche Discussion

Many areas have at least DOUBLED their snowpack depth in the past few days. Anytime that happens, there are usually avalanches, and today that proved true. Folks reported touchy conditions with lots of collapsing and cracking at Mission Ridge, with patrol triggering wide avalanches in the 1.5-3ft deep range. These slides were running on a thin crust from around 11/25, and many stepped down to, or ran on the ground (or on basal facets from 11/22). In Icicle Creek, there were multiple reports of whumphing tied to basal facets (11/22) in different locations as low as 3,600ft on North facing slopes. An observer at Holden also reported some whumphing on a layer of surface hoar from 11/22. All of this is strong evidence that this layer is not ready to be trusted yet, and could produce surprising and wide avalanches. 

Here's a brief season history: A couple of substantial storms came through in early November. A two week dry period followed, with a strong inversion in place for much of the time. This created weak, faceted snow on shaded aspects, and surface hoar grew large in some areas. Snowfall began again on November 22nd, with some very cold temperatures following. The recent round of active weather and snowfall began around November 25, starting as rain then quickly turned to snow. These weak layers and slick crusts were buried by a series of storms in mid to late November, and recently we've received 2-4ft of snow.

It's still early season, and the snowpack is relatively shallow and unconsolidated. With DEEP, unconsolidated snow out there, make sure to stay within earshot or visual of partners. Tree wells are getting deeper, and plentiful buried snags, creeks, and rocks exist. If you are out and about in the mountains, let us know what you find by submitting an observation.

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