Bollettino valanghe

East Slopes North

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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In sintesi

Another round of wind and snow will make it easy to trigger avalanches and some could be very large and destructive. The Washington Pass area is experiencing dangerous conditions after a major avalanche cycle involving older weak layers. Use extra caution to keep your distance from areas where avalanches can start and stay well out from under large avalanche paths.

Problemi valanghivi

  • Wind Slabs

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

    Watch for triggering avalanches on leeward sides of ridges and wind-exposed features. If you look closely, you may see blowing snow indicating where fresh wind slabs are being deposited. Steer around areas of deeper drifts and stiffer snow on slopes 35 degrees and steeper. Consider the potential to trigger very large and unsurvivable avalanches on more deeply buried weak layers. See below.

    A midday shift from east flow to stronger southwesterly winds should form fresh slabs at upper elevations. You may still be able to trigger slabs that were reactive on Thursday, also formed from southwest winds. These avalanches could be big enough to bury you.

    (12/29/2022) Cracks shoot through fresh wind slabs high above Early Winters Creek near the Silverstar trailhead. 7,000ft, SSE Photo: Josh Hirshberg

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    Stay out of big start zones and well out from under large avalanche paths where you suspect buried surface hoar and well-developed older weak layers. Persistent slab avalanches are difficult to predict and can break in surprising ways. You may be able to trigger them where the weak layers are most developed and especially where wind-drifted snow continues to put stress on them.  You can dig and use snowpack tests to identify these layers. 

    We have good evidence that a cycle of very large, natural avalanches occured starting around the 24th and continued to as recent as the 27th or 28th. You're most likely to trigger these avalanches during or just after natural avalnche cycles. Snow profiles suggests that these avalanches involved the Dec 8th buried surface hoar (3ft below the surface) and possibly sugar-like facets from November near the bottom of the snowpack. If you're traveling east of the Cascade crest, near the Silverstar drainage, or near and east of Mazama, consider that avalanches could potentially involve most of the season's snowpack.

    (12/28/2022)

    A very large avalanche (D2.5) that occurred during the Christmas Storm. Potentially ran on weak, faceted grains from November. Vasiliki Ridge, NW, 7,400ft

    Photo: Jeremy Allen

Avalanche Discussion

Observers reported at least 4 very large, size D2.5-3.5, natural, slab avalanches that ran roughly between December 24th and 27th. At least one very large avalanche may have involved weak layers near the bottom of the snowpack, though we haven't been able to confirm this.  A deep crown was reported in the Vasiliki Ridge area on a northwest aspect around 7,400ft. On Thursday, observer Willie Webster,  reported a couple of these on northwest aspects along with smaller avalanches in storm snow in the Hairpin Valley vecinity. Willie's snow profile nearby found the problem layer to likely be a layer of surface hoar, believed to be buried 12/8, over 3 feet below the surface. On Tuesday, I found similar, propagating test results on the 12/8 surface hoar near the confluence of the Cutthroat and Early Winters dranaiges. On Wednesday, a long-time avalanche professional reported occasional collapses in the mountains just north of Mazama. See photos and video below. 

Heavy snow and rain starting on December 23rd brought 3.5 " of water equivilent (a conservative measurment) to the Washington Pass weather station through the 27th. A thick crust was buried on the 25th and this new weight activated weak layers that have been lurking for many weeks. The crust is now about 1.5 feet below the surface near Washington Pass, and as shallow as 6 inches near Mazama. We're still gaining an understanding of the full extent of the recent avalanche cycle. If you see avalanches, please slet us know by submitting an observation.

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