Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
3 · Marcato
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In sintesi

Warm wet weather will combine with a cold dry snowpack to produce very dangerous avalanche conditions Saturday, especially at mid and upper elevations. This won’t be the time to try and sneak around the hazard. Instead, better to just get out of its way by staying off of and out from under steep open slopes.

Problemi valanghivi

  • Wet Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    1.5–2.5

    This storm checks all the boxes. Warming temperatures, significant precipitation, rain, and strong winds will all impact a very cold, dry, and layered snowpack. Not surprisingly, we suspect this big change should result in big problems… natural avalanches. While these ensuing slides could take many forms and fail on any number of layers, the travel advice remains the same. This won’t be an easy hazard to manage. So, give it a wide berth. Where you find rain or very heavy snowfall, stay away from places avalanches start, run, and stop. 

    At lower elevations, another round of freezing rain should make avalanches less likely. However, there is plenty of uncertainty with this weather forecast, and spatial variability will only compound the issue. If you encounter rain below treeline, anticipate a significant increase in the avalanche danger and the possibility for natural loose wet and wet slab slides.

    (12/23/2022)

    Example: This natural wet slab avalanche below treeline at Mt Rainier. NW 3800ft may serve as a clear indicator of what's to come as warmer temperatures and rain continue to impact the snowpack. 

    Photo: NPS Rainier Rangers

Avalanche Discussion

While Saturday’s forecast carries with it plenty of uncertainty due to the weather and snowpack, at some level it’s simple. We know we have a very cold, dry, and layered snowpack that will likely not handle the sudden change to warm rainy weather very well. Through the course of the day you may see storm slabs, wind slabs, loose wet, glide, wet slab, and even persistent slab avalanches. Be ready to adapt to rapidly changing conditions by choosing terrain with plenty of options that let you safely retreat to your car.

The biggest variable will likely be the east winds and their ability to keep the lower elevations cold. If this continues freezing rain may coat the snow with ice and limit the avalanche hazard. However, if the warm air wins the battle, rain could quickly increase the hazard resulting in higher than forecasted avalanche danger.

This will be the first real rain the snowpack has seen since mid-November. Several older weak layers still exist. While we haven’t really seen much in the way of avalanches on any of these layers, this storm could wake them up. This could occur when water percolates down into the snowpack or if smaller natural slides act as large triggers on these once dormant weaknesses. If avalanches fail on these older snow layers it could result in much larger avalanches that travel further into their runout zones.

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