Bollettino valanghe

Olympics

Northwest Avalanche Center
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In sintesi

Winter's return will bring snow, wind, and a chance of avalanches. Look for blowing snow, pillow-like deposits, recent avalanches, and shooting cracks, and give a wide berth to steep open slopes nearby if you see any of these signs. Below the new snow may lurk a low likelihood but high consequence threat of a dangerous wet avalanche. Manage that problem by either avoiding steep and open slopes at the middle and upper elevations, or by limiting your time spent on or below any avalanche paths.

Problemi valanghivi

  • Wind Slabs

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

    New snow and moderate winds will form fresh wind slabs on lee slopes. The slabs are most sensitive during and soon after formation, which should be the case for most of Friday. Blowing snow will be a sure clue that there could be trouble. While most slabs should be relatively shallow, slabs could be deeper in favored locations below sharp ridge lines and cornices, at the base of cliffs, or at the top of gullies. You can use small test slopes, hand pits, and uptrack tests to help gauge reactivity. If you see shooting cracks, see chalky drifts, or feel hard over soft snow, you'll also know you've found one.  Any triggered wind slab could gouge into wet mushy snow below or trigger a dangerous wet slab avalanche. 

    (3/21/2025)

    Signs of wind affected snow and potential wind slabs. 

    Photo: Dallas Glass

  • Wet Slabs

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

    We are using wet slab as a catch-all for the full buffet of wet avalanches that may still pose an issue on Friday: wet slab, glide, wet loose, and cornice failures. Copious amounts of rain fell in the Olympics since the 24th. With the road closed for most of that time and limited visibility today, we don't know if there was a cycle here. What we do know is if a deeper wet avalanche were to release, it would be large and possibly unsurvivable. Throughout the Cascades, including twice yesterday at Crystal Mountain, very large wet slab avalanches have released, broken many feet deep and hundreds of feet wide, and descended up to thousands of feet into valley bottoms below.  These slides can release on their own, without warning, many days after rainfall.  Time and cooling temperatures are helping ease the danger, but we can't rule it out just yet. 

    These avalanches would most likely originate at the upper or middle elevations. In addition, cornices are sagging and if they fail, they could trigger a slab or loose avalanche below. We won't be surprised if we don't hear of any new wet slab avalanches on Friday, but we also wouldn't be totally surprised if a large and destructive one released naturally. How to manage uncertainty like that is a personal decision, but recognize that the problem could be out there.

    (3/26/2025)

    A very large wet slab avalanche was explosively triggered by Crystal Pro Patrol on Wednesday afternoon. This slide was 300-400ft wide, broke 4 to 6ft deep, and appears to have run on the old 1/10 crust. While this may be an outlier result, it does nothing to inspire confidence in the state of the snowpack. Until we get a solid refreeze at depth, there will a be chance of a large and unpredictable wet slab avalanche.

    N, 6800ft. WS-AE-D3-O

    Photo: Crystal Pro Patrol

Avalanche Discussion

When the snowpack is uncertain, terrain is the answer. On it's face, this storm doesn't look like much. The problem it is covering up, however, is the hardest problem to forecast for. While peak wet instabilities have likely passed, free water in the snowpack may still be percolating to parts unknown, and we don't fully trust it yet. Ultimately, we need a bit more time with some cold temperatures for the water deeper in the snowpack to freeze up or complete its journey, one way or another. Choose simple terrain with low consequences tomorrow as you navigate the overlapping problems.

On Friday, ONP Rangers found wet snow down to 55 cm and a solid lower pack below that, a good sign to be sure. They also noted broken cornices and a beat-up snowpack, with many bare spots on south-facing slopes. The snow surface underneath the new snow is unlikely to be ski-supportable in all places Friday, perhaps leading to some punchy conditions. Also, keep in mind that the new snow may barely cover up old uneven debris. If you are out, please share what you see with us and your local backcountry community.  

This will be the last weekend of daily avalanche forecasts for the Olympics this season. 

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