Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

Avalanche hazard should increase as you ascend in elevation on Monday where both wet and dry avalanche problems may be found. Steer around wind-drifted piles of snow where you could trigger an avalanche more easily and head for low angle terrain if you notice fresh avalanches containing wet and heavy snow.

Problemi valanghivi

  • Wind Slabs

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

    Winds on Monday could create new Wind Slabs or thicken existing slabs at upper elevations where cold dry snow still exists. At middle elevations, warm temperatures or possible rain could help to destabilize recently created slabs, possibly triggering wet avalanches. Look for Wind Slabs to be more reactive near rocky features such as gullies and cliffs, on convex rollovers, or leeward slopes near ridgelines. Some of these slabs may be sitting on buried weak snow grains, causing them to break in surprising ways, meaning you may need to manage them a little differently than what you may be used to up at the Pass. Take some time and dig down to the 1/13 crust to look for the existence of weak snow or poorly bonded interstorm layers before committing to terrain. Use test slopes to check the reactivity of all of the snow sitting atop the crust to see how it reacts to your weight. As you travel, look for textured surfaces, smooth pillow-like piles of snow, or fresh cornices to key you into wind-loaded features you should avoid.

    (1/31/2021) This Wind Slab was intentionally triggered on a wind-loaded convexity in the Kendall area on Sunday (1/31). The slab initially broke on a density change before stepping down and failing on the 1/13 crust.

  • Loose Wet

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

    Should be another relatively warm day up at the pass on Monday as freezing levels are expected to reach 5000 feet. On Sunday, warm air made its way into the zone and caused a lot of rollerballing and a bit of loose wet activity as snow shed from trees and rocks. This could help minimize the impact of warmer temperatures and possible rain at the lowest elevations on Monday. Locations with snow getting wet for the first time should be where you find the highest likelihood for wet avalanche activity. Look for these slides to start at a point, such as where snow sheds off trees and rocks, and then fan out as they move downhill. These slides are capable of entraining lots of snow and even triggering slabs as they descend. If initiated, they may gauge down and involve all of the snow above the 1/13 crust, possibly breaking as slabs if persistent grains are present. Head for low angle terrain away from steep slopes above you if it starts raining on dry snow or you notice fresh avalanches and rollerballing.

    (1/31/2021) Look for snow shedding from trees and rocks, possibly causing rollerballs as an indicator that wet avalanches may follow.

Avalanche Discussion

Weak snow grains in the form of buried near-surface facets and possibly buried surface hoar have been at the top of our concern list as snow depth above the 1/13 AR crust has increased. There is currently around a foot of snow above the 1/13 crust on average, with areas of deeper wind drifted snow or wind-scoured areas containing considerably less. In many areas, the 1/13 crust is extremely stout, and although weak snow can be found within it and below it, we are not currently concerned about these layers. 

Reports have slowly trickled in that wind-loaded pockets have been propagating widely within the zone and observations continue to confirm the existence of persistent snow grains. On Sunday, NWAC members were able to trigger a Wind Slab on a test slope that failed on a density break before stepping down to the AR crust where rounding near-surface facets were found. Recent slab development due to the warmer temperatures now means that in areas where buried weak grains exist, we now have the 3 elements needed for slab avalanches: a slab, weak layer, and bedsurface. How reactive and widespread this setup is at the pass remains to be seen, but for now, consider dialing back your terrain choices from what you may normally pursue at Moderate danger. Look for those red flag signs of instability, such as shooting cracks and whumpfing collapses as indicators that you could be dealing with a persistent weak layer. And take some time to dig down to the 1/13 crust, perform some tests and look for the existence of weak snow grains. If you do not find them, you should not immediately rule out their existence. Instead, continue to collect more information and ease into terrain. Thanks to everyone who has submitted public observations this weekend as we navigate a bit of uncertainty around the snowpack. We’d love it if you kept them coming! Submit a public observation here. 

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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