Boletín de aludes

Snoqualmie Pass

Northwest Avalanche Center
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Peligro de aludes

Fri
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 4 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

On Thursday, there should be another round of fresh snow and some light winds at Snoqualmie Pass. Tread carefully on steep or convex slopes where you’re more likely to trigger a slide in wind-drifted snow. The potential for dangerous wet avalanches still lingers, possibly threatening lower-elevation terrain.

Problemas de aludes

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2

    The most likely location for you to trigger an avalanche on Thursday will be in wind-loaded terrain. Some Wind Slabs may be buried under freshly fallen snow, hiding from view. So you should try to feel for subtle changes in the snow’s stiffness to help identify where they're lurking. Using other visual clues such as freshly built cornices or new drifts behind objects can help you identify which way the wind was blowing. The wind often likes to deposit snow at the base of cliffs, the side of gullies, or on convex features. And of course, the leeward side of ridgelines is an obvious place to find wind-loaded slopes. Now that you know what to feel for and where they’re more likely, you can start to identify wind-loaded features to avoid.

    (12/28/2022) Stomping on a wind-loaded pocket produced cracking on this test slope on 12/28. Photo: Andy Harrington

  • Glide Cracks

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Unlikely
    Tamaño
    1.5–2.5

    At mid to upper elevations, there are still plenty of wet unconsolidated grains under the new snow, keeping Glides on our minds. Multiple Glide avalanches occurred in the past few days, the most recent of which was on 12/27. These unpredictable and difficult to forecast avalanches should be trending downward as temperatures continue to cool. However, the right piece of terrain or the right trigger such as a failing cornice or another avalanche could still set one of these in motion. Since these slides are so hard to predict, your best management tool is to identify likely Glide terrain and avoid it. Open slopes over 35 degrees, especially if you see a crevasse-like crack, or hanging blocks of snow and ice on smooth rock faces are the most likely locations for one of these honkers to fail. Any Glide avalanche at this point would most certainly be large enough to bury or kill you and could run far distances down into the below treeline band.

    (12/26/2022)

    A glide avalanche in Shot 6 at Alpental, plus a separate Glide crack where the snow has not yet released. 

    Photo: Alpental Pro Patrol

Avalanche Discussion

It was a welcome sight for winter lovers to see freshly falling snow at Snoqualmie Pass on Wednesday. Roughly a foot of new snow accumulated over the Christmas Crust and was found to be generally well bonded in most places NWAC forecasters had the chance to look. Another shot of snow should impact the zone on Thursday, increasing the depth over this crust and potentially adding interstorm layers for you to investigate. If the pass ends up overproducing on water and the snow is piling up, you could see higher avalanche danger as the likelihood of triggering an avalanche on a slope over 35 degrees increases.

At lower elevations, the Christmas Crust is stout (~7” thick) and boot-supportable. It’s actually 2 different crusts melded together into one block with some slightly softer grains in the middle. Below the crust is mostly dry snow in many locations.

As you ascend in elevation, you’ll reach a point where freezing rain over the holiday weekend didn’t reach (~4500’) and you’ll find that the Christmas Crust is made up of two very thin (~1cm) crusts with softer snow between them. Below these crusts, are unconsolidated moist grains due to the soaking rains. The moist snow has not yet started to freeze from the top down and it will take a bit of time with the new snow helping to insulate it. The Christmas Crust was not supportable for walking when NWAC forecasters stepped out of their skis and the new snow showed some signs of failure during small column tests near this interface. 

Poor visibility on Wednesday didn’t help with the spotting of avalanches, but public observations indicate that the winds were gusting near ridgelines and in some areas, snow was scoured down to the Christmas Crust. A few older crowns from the previous avalanche cycle were spotted, and some fresh debris was seen coming out of some rocky chutes. The most notable debris spotted was in a meadow in the Alpental Valley bottom due to the Snoqualmie River surging during the storm. Large wet piles of snow and even some broken trees were seen. A good reminder of the uniqueness of this storm.  Snowshoers on the PCT noted that large chunks of ice suddenly gave way from a frozen waterfall which helps reiterate the difficulty in predicting wet snow problems. As we slowly make our way out of this stormy and active period, you could find some unusual conditions or difficult travel in places. We’d like to hear about them or anything else you’re seeing out there. So please submit a public observation.

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