Boletín de aludes

Snoqualmie Pass

Northwest Avalanche Center
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Peligro de aludes

Fri
Alta montaña
3 · Notable
Límite del bosque
2 · Moderado
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 6 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

If you are not standing on a firm crust on Thursday, then you are in snow capable of producing dangerous avalanches. Look out for increased hazard in areas where the wind has blown the snow into deeper piles as you ascend in elevation. If you are on a firm crust and fall, you could potentially slide a long way. 

Problemas de aludes

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    2

    Winds were significant at Snoqualmie Pass as we transitioned out of the atmospheric river event, with wind speeds over 100 mph captured at NWAC’s weather station on top of Alpental before power outages knocked out communication. These winds were certainly strong enough to transport any cold and dry snow onto leeward slopes or toward the sides of gullies and bases of cliffs to form dangerous Wind Slabs. The main problem these winds may have had was finding cold dry snow to transport. You’ll have to look to upper elevations above the rain/snow line to find this snow, and subsequently find Wind Slabs. We have some uncertainty around what elevation this transition takes place at, but it does exist. When you find it, you’ll know immediately and you should be on the lookout for wind-textured snow surfaces, freshly built cornices, and smooth pillow-like piles of snow to help you identify wind-loaded slopes that you should avoid. 

    (1/13/2021) Plenty of crowns on the arm of Chair Peak, with debris running down as far as common travel routes. A lot of these crowns are at the base of cliffs where wind drifted snow frequently accumulates. [Photo: Charlie Hagedorn]

  • Glide Cracks

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2–3

    As we just alluded to in the Wind Slab problem, there was a lot of rain the past few days up at the pass, resulting in a significant wet avalanche cycle. The snowpack is pretty beat up below the rain/snow line at this point, but may still be capable of producing surprising wet avalanches on Thursday as freezing levels rise. Although listed as Glide, other wet snow related avalanches such as Wet Slab and Wet Loose are still on our minds, as these problems are often intermingled. Wednesday's cool temperatures with help from the return to East flow on Thursday should help to minimize wet avalanche activity, but the reality is that the snowpack needs time to adjust to all the recent rain. It remains possible for large or even very large Glide avalanches to occur naturally. Avoid traveling underneath glide cracks, which appear to look like crevasses. 

    If you make it to the upper elevations where cold dry snow exists, and find that the sun is out and snow surfaces are getting wetted for the first time, look out for wet avalanches. Avoid steep rocky slopes and cliff bands, where snow could shed from above. Even tree bombs could trigger these slides. Wet Loose avalanches are capable of entraining lots of snow, triggering slabs, and traveling far distances as they descend. Those fresh cornices that were formed by the strong winds could also fall if the sun gets to them, give them a wide berth. Conditions like these bring quite a bit of uncertainty and are hard to assess. Travel cautiously and build in a wide margin for error.

    (1/13/2021) This Glide avalanche occurred at Alpental on a slope that is known for these types of slides. On the right side of the picture, you can see a Glide Crack on a slope that has not yet climaxed. [Photo: Charlie Hagedorn]

Avalanche Discussion

Well that escalated quickly, now didn’t it? Seems like we were in a winter wonderland just a short time ago with plenty of cold dry snow to play in, then all of a sudden, we are transformed to carnage. Observations have been limited, including automated weather station data, but we are slowly gathering information. There have been large to very large avalanches throughout the zone during this cycle, with both wet and dry snow avalanches occurring up to size D3. Rockface, a classic Glide indicator slope at Alpental, has climaxed down to the rocks. Apart from the in your face avalanche hazard, roads are flooded, power has been knocked out, trees are breaking under the weight of snow and ice, and creeks are running high. If you venture out into the mountains on Thursday, you need to be prepared for things to look very different than just a few days ago. With all this wetted snow and cooling temperatures, the snowpack should be freezing from the top down, potentially creating slide for life conditions. Unless of course the skyrocketing freezing levels and sunshine are able to get to the snow surface and keep things wetted. Regardless of how the weather shakes out, take it easy out there and realize that there will be other days to achieve your dreams. Since I’m sure you won’t be spending a long day in the mountains, you may as well get home early and share what you found on our public observations page.

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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