Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

Fri
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Keep your eyes open for slopes where the wind piled the snow deeper as ascend in elevation. Drifts behind trees, rippled snow surface textures, and fresh cornices can serve as clues to steer away from nearby steep terrain. As the day warms up and you feel the sunshine, watch for new rollerballs and natural loose avalanches occurring on nearby steep rocky slopes.

Problemi valanghivi

  • Wind Slabs

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

    Several human triggered wind slab avalanches occurred Tuesday and Wednesday at Snoqualmie Pass. While these slabs aren’t widespread, if you start to notice deeper snow over the recent crusts or feel the snow becoming stiff,  you may have found them. Strong westerly winds during the most recent storm formed wind slabs at mid and upper elevations. On Wednesday, moderate southeasterly winds formed fresh shallow deposits on slopes previously wind-scoured. That leaves us with a criss-cross of new and older wind slabs on a variety of aspects. When you notice a textured snow surface or see wind drifts, be leery of steep and convex slopes where you anticipate wind loading occurred. If you travel into more alpine terrain, you may find wind slabs larger and easier to trigger.

    (12/23/2020) Blowing snow from moderate southeasterly winds was forming thin new wind slabs. Chair Peak, 5200' N aspect.

  • Loose Wet

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

    We expect pretty warm temperatures for late-December Thursday. When you combine this with the recent snow and a mid-winter sun, you can anticipate natural loose avalanches occurring on very steep sunny slopes. It will take a bit for warmer weather to overcome the morning inversion, but once it does, look for the snow shedding from rocks and trees. This may serve as your first clue to the increasing potential for loose avalanches. When you see new rollerballs or fresh fan-shaped debris, steer around similar slopes. Don't let a small loose avalanches push you into a creek, over a cliff, or through trees. 

    (11/27/2020) Example: Pinwheels at Mt. Rainier after rising freezing levels and the sun came out a few days after a storm. [S aspect 5400']

Avalanche Discussion

This recent storm left 15-25cm of light dry snow over a very firm and supportable crust. We anticipate any avalanche activity to occur within the recent snow above this icy layer. Potential buried persistent weak layers in the mid-snowpack (12/09 crust and 12/13 facets) were thoroughly tested by last weekend’s rain events. Several crowns and debris piles were observed around Snoqualmie Pass, though this zone does not appear to have experienced the same large avalanche cycles as the Stevens Pass and West South zones. 

You could experience very different temperatures Thursday depending on your west to east location across the zone. Expect everywhere to be a bit chilly at the trailheads in the morning as a strong temperatures inversion keeps the lower elevations cold. As the day wears on, you’ll find warmer temperatures pushing into the western half of the zone and at upper elevations. Sites further east could remain under the inversion longer during the day. 

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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