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

Danger from human triggered avalanches may continue on Thanksgiving Day after a storm dropped over a foot of snow in the mountains of Snoqualmie Pass. There were multiple reported human triggered avalanches on Wednesday, demanding our attention and reminding us to ease into terrain after a storm. If you head into the mountains, remember that the biggest red flag for avalanches is recent avalanches, and we just had a lot of them. Take some time and make your own observations that can be applied to any piece of terrain you are thinking of traveling on.

Problemi valanghivi

  • Storm Slabs

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

    Storm Slabs may continue to be reactive on Thursday as we transition away from a storm that brought 1.5” of water in 24 hours. Slabs may be deeper and more reactive as you ascend in elevation or where the wind was able to push snow into deeper piles. Look to avoid these deeper piles which are most commonly found on leeward slopes, at the base of cliffs, or on the sides of gullies. Take the time to dig some hand-pits and play on small test slopes to give you an indication of how sensitive slabs may be or how well they are bonded to the old snow. A mid-storm layer was the main culprit of many failures on Wednesday so take a look to see if this layer is still active.  If you find that the snow is poorly bonded or experience clues of unstable snow such as shooting cracks or whumpfing collapses as you travel, seek out lower angle terrain.

    (11/25/2020) This slab was triggered by skiers ascending the closed Alpental ski resort on Wednesday.

Avalanche Discussion

We had a pretty active day up at Snoqualmie Pass on Wednesday. We exceeded forecasted water numbers and there were many human triggered avalanches reported, with a few being as large as D2. Although there were no confirmed reports of natural avalanches, our limited observations lead us to believe that we had a natural cycle during the storm. It appears that most reported avalanches failed on a mid-storm layer about 2 inches above the old snow interface with good propagation. Alpental Pro Patrol reported that you could trigger an avalanche on almost any micro-feature in the valley and that they witnessed multiple ski tourers triggering avalanches as they both ascended and descended. One slide in the Alpental ski resort was reported via our observation platform and states that it was remotely triggered by a ski tourer and that the crown wrapped around terrain features. Now that you have this information, if you decide to step away from the dinner table and venture into the mountains, be prepared to make conservative route choices and be on the lookout for lingering slabs. Remember to keep an eye out for freshly built cornices, textured snow surfaces, or pillow-like piles of snow to help to identify potential wind loaded areas. And if by chance the sun comes out for a prolonged period of time on Thursday, take note of how the snow surface may be changing and keep the possibility of wet avalanches in the back of your mind. If you see rollerballs or snow shedding from trees, head for shaded or lower angle terrain. Lastly, keep in mind that it is still early season and there are plenty of natural hazards to avoid despite a great start to the snow year, especially at lower elevations.

 

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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