Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

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.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    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, hard wind slabs were observed 1000’ below ridgeline on Wednesday showing that all elevations could harbor the problem.

    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.

    (2/18/2023)

    Signs of wind loading to look for on Thursday.

    Photo: Dallas Glass

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    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.

    (2/2/2025)

    This avalanche released after a audible whumpf. The slide failed on facets over a crust and released the entire width of the feature. NE, 3700ft

    Photo: Summit at Snoqualmie Professional Patrol

Avalanche Discussion

NWAC forecasters and snow professionals all noted significant blowing snow on Wednesday and multiple tour plans were changed in response. Wind slabs are already reactive as evidenced by the two skier-triggered wind slabs in the zone and things will only get more dangerous on Thursday as 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. 

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