Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Fri
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
1 · Debole
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In sintesi

Sustained strong winds will continue to form fresh, reactive wind slabs that a person is likely to trigger, and in some areas, natural avalanches may occur. Look for blowing snow, textured surfaces, and pillow or lens-like deposits, and avoid steep slopes where you see any of these signs.  Fresh wind-loading may increase the chances of triggering a high consequence persistent slab avalanche on steep open slopes facing west, north, and east.

Problemi valanghivi

  • Wind Slabs

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

    With tons of soft snow available for transport, we expect significant slab formation despite the low precipitation totals overnight and on Thursday. Some of these slabs could be 1-2 feet thick, hard, and connect widely across the terrain. On many slopes, they may fall on weak surfaces which could make them more reactive and/or propagate even wider. Likely locations include below ridgelines and cornices, at the bases of cliffs, entrances to gullies or chutes, and on gully sidewalls in cross-loaded terrain. While areas closer to ridgeline will likely have thicker slabs, mid-slope well below ridgeline could be suspect as well as strong winds build slabs lower down in the terrain.

    While wind slab is the most likely avalanche problem you will deal with on Thursday, they could also awaken the persistent slab below and cause an even more dangerous and deeper avalanche. By avoiding freshly wind-loaded terrain, you will greatly reduce your chances of triggering a persistent slab.

    (12/8/2024)

    Visual clues such as actively blowing snow, fresh cornices, or pillow-like drifts can help identify wind-loaded slopes to avoid.

    Photo: Andy Harrington

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2

    Weak layers lurk beneath a 1.5-3.5ft thick slab in wind sheltered areas and an even thicker slab in freshly wind-loaded start zones. The likelihood of triggering a slide on these layers is low, but low probabilities don’t matter to the person who draws the short straw. 

    If you decide to roll the dice, stack the odds in your favor. For one, don't travel on steep slopes that are freshly wind-loaded as these are the most likely locations to trigger the persistent slab. If you are considering non-wind loaded steeps on the shaded half of the compass, discuss the consequences of a slide with your partner. Hedge towards simpler, smaller, and lower-angle. Choose planar and supported terrain with clean runouts and no terrain traps, only expose one person at a time, and minimize your exposure on the ascent. Keep in mind that areas where the slab is thinner, such as around rocks, trees, and locally wind-scoured spots may act as trigger points. Complex terrain often holds a dangerous combination of thicker and stiffer slabs with locally thin areas on the slope.

    (2/1/2025)

    This intentionally triggered persistent slab in the West South zone propagated the entire width of the feature. It failed on facets over a thin crust. ENE, 6200ft, SS-ASc-D2-R3-O, 20-24 in deep, 200 ft wide.

    Photo: Dallas Glass

Avalanche Discussion

Significant wind transport was observed on Wednesday in the West South and conditions will only get more dangerous on Thursday as slab size and reactivity both increase along with the wind. Coupled with the cold, expect biting wind chills to add additional complexity and risk to the day.

While wind slabs will be front and center, the persistent weak layer persists, and new load could increase reactivity. Whether for the wind or persistent slab, remember that the snowpack doesn't care if the new load comes from the sky or an adjacent slope, it is all still load. Don't get caught off guard by reactive avalanche conditions on Thursday. It's a good day to add a wide safety margin and seek out the fantastic snow in lower-angle shaded terrain. 

Regioni coperte