Bulletin d’avalanche

Snoqualmie Pass

Northwest Avalanche Center
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Danger d’avalanche

Wed
Alpin
3 · Marqué
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 2 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Another quick storm will drive dangerous avalanche conditions on Tuesday, especially on exposed slopes where the wind will drift snow into deeper slabs. Treat steep slopes as suspect unless you can confidently prove otherwise. Warm temperatures should also keep wet avalanches near the rain/snow line on your mind.

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    By Tuesday morning, 6–8 inches of new snow could accumulate above 5000 feet, accompanied by strong, shifting winds and warming temperatures—all good conditions for avalanche formation. While most avalanches are expected to involve the new snow, there’s a chance they could step down into the 10+ inches of snow from Monday. Rollovers and unsupported terrain features are especially suspect. In wind-loaded areas, new slabs may form on top of older, unstable ones, breaking up to 3’ deep and carrying major consequences. Identify slabs by feeling for hard over soft snow and looking for blowing snow, textured surfaces and chalky pillow-like drifts.

    If you're considering steep terrain, assess stability carefully. In non-wind-affected areas, hand pits, uptrack tests, and safe test slopes can provide clues about slab presence and reactivity. Shooting cracks or block failures are signals to avoid adjacent steep slopes. In wind-loaded zones, avoiding steep slopes is not only the safer choice until these slabs stabilize, but it will also lead you to more enjoyable snow!

    (2/22/2022)

    A slab avalanche triggered on a wind-exposed slope. Avalanches like this are likely on Tuesday, especially in the morning hours.  

    Photo: NWAC Public Obs

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–1.5

    Close to the rain-snow line, wet and mushy snow may sit on a newly formed crust from Monday, or it may rest on deeper soggy old snow. The potential size of wet loose avalanches will depend on the depth of wet snow, and they are most likely to occur on very steep slopes. Natural releases are possible, especially on south-facing slopes if the sun makes an appearance.

    While generally easier to manage than slabs, wet loose avalanches can still be hazardous, particularly if they knock you off your feet in dangerous terrain or trigger deeper slab avalanches. Watch for rollerballs, pinwheels, and sinking into boot-top snow—these are clear warning signs. Avoid traveling on or lingering beneath steep slopes showing signs of wet loose avalanche activity on Tuesday.

     

    (2/16/2024)

    An example of wet loose avalanche activity during clear skies on the southern half of the compass.

    Photo: Julz Holder - Grounding Truth

Avalanche Discussion

Monday night's storm feels quite similar to Sunday's and will create a similar blend of avalanche conditions for you to manage on Tuesday. Avalanche danger should be the highest in the morning hours and decrease as we move further away from the peak of precipitation. 

On Monday, Summit at Snoqualmie Pro Patrol observed a natural slab avalanche in addition to a short lived and small wet loose cycle during periods of sun. Encouragingly, they found the new snow bonding reasonably well to the crust below. They also noted a newly formed crust below 4000'. And, as many have reported, travel below 4000' remains grueling, though upper-elevation travel should be nicely refreshed.

With this next storm, the Pass remains in a see-saw battle with fluctuating snow levels and the persistent possibility of unfrozen snow falling from the sky (rain). Small changes in snow levels could significantly impact accumulation, wet loose issues, bonding, and wind effects, bringing a heavy dose of uncertainty to Tuesday's forecast. Plan for variability. Be ready to assess conditions as you go—you may find more or less snow, a new crust, higher or lower rain-snow lines, and all of these permutations will affect avalanche conditions. A safe tour plan will give you opportunity to evaluate the conditions while minimizing your exposure and provide for many different options depending on what you find.

With an active weather pattern continuing through the week, let’s hope we eek out a few feet at pass level to improve access and conditions for everyone!

Régions couvertes