Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

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

Human triggered avalanches will continue to be of concern on Wednesday at Snoqualmie Pass as we transition out of a major storm cycle. Steer around wind-drifted piles of snow where you could trigger an avalanche more easily. If you encounter wet and weak snow surfaces, head for lower-angled slopes and be aware of the terrain above you.

Problemi valanghivi

  • Wind Slabs

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

    The wind has been transporting snow above the rain/snow line these past few days at Snoqualmie Pass building Wind Slabs, and more recently at all elevations. Public observations on Tuesday confirm that multiple D2 Wind Slabs were triggered by humans within the Snoqualmie Pass zone, so keep them on your radar heading into Wednesday. Wind Slabs often develop on leeward slopes, at the base of cliffs, or on the sides of gullies, but you can look for fresh cornices, textured surfaces, or smooth pillow-like piles of snow to help you determine more specific locations to avoid. As you ascend in elevation above the previous rain line from this weekend, slabs could be much larger and possibly more reactive. Take note of clues of unstable snow such as shooting cracks or whumpfing collapses as you travel, and use small test slopes to test for slab potential and poor reactivity. If you notice any of these signs of instability, steer around wind-loaded slopes.

    (12/22/2020) This Wind Slab was human triggered on Tuesday on a common ascent route in the Alpental Valley.

  • Loose Wet

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

    Rising freezing levels throughout the day and some sunshine could combine to trigger a few Wet Loose avalanches on Wednesday on solar slopes. With some East winds bringing cold air through the passes at lower elevations, it could take longer to destabilize the snow surface to create avalanches. If the East flow is in effect, you could find that it is chilly and cloudy by your car, but warm and sunny as you ascend in elevation. In short, if you feel the snow surface heating up, you should be aware that Wet Loose avalanches are possible and of your exposure to avalanche terrain. If you notice rollerballs, snow shedding from rocks, or see fan-shaped avalanche debris, seek out shaded terrain away from sun-exposed slopes above you.

Avalanche Discussion

It was a wet and wild weekend at Snoqualmie Pass, but Monday night brought some cooling temperatures and a nice shot of snow (~8 inches) with gusty winds to help us forget about the almost 4” of rain we received. This new snow has changed our focus to new snow avalanche problems from the Wet Slab problems we were concerned about over the weekend. The highest elevations in our zone have been receiving snow all along, and we have yet to make it to these elevations to determine how the snowpack was affected. But it's a safe bet that slabs should be larger and potentially more dangerous as you ascend in elevation. One thing we can say is that we put the weak snow crystals (12/13) above the 12/9 crust to the test at all elevations with this previous storm. Even though reports of what actually happened out there are still slow to trickle in, we feel confident that a natural avalanche cycle did happen. We are basing this off NWAC team members finding multiple storm interfaces of concern at Snoqualmie Pass on Friday and Saturday, observations from adjacent zones where widespread natural avalanche activity occurred, along with pictures and observations submitted on our public observation platform. These adjacent zones to our north and south contained a similar snowpack structure to Snoqualmie Pass prior to Saturday night’s storm. Does all this mean that this layer is dead and we can take it off our radar? I wouldn’t go that far quite yet, but avalanches on this layer appear to be trending toward unlikely.

As we move into the holiday week and some nicer weather, we anticipate a busy few days in the Snoqualmie Pass backcountry. Before heading into consequential terrain, think about what we do and do not know about the snowpack structure and this previous storm. Take some time and do a little digging where you are looking to recreate to help you determine if the 12/13 layer is still present or if there are any interstorm layers that are reactive to your weight. The likelihood for natural avalanches is decreasing, but as we saw on Tuesday, conditions could still be ripe for human triggered avalanches to occur, particularly if you find yourself in terrain that did not slide during the previous cycle or has recently been affected by the wind. When in doubt, dial back your terrain choices.

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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