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
1 · Debole
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Non aggiornato — questo bollettino è scaduto 2 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Happy new year!

Lots of soft snow on the surface and a quick hit of wind and snow will keep the avalanche hazard elevated at the Pass on Wednesday.  Look for signs of wind-loading like blowing snow and chalky drifts, assess for reactivity carefully before committing to big terrain, and consider giving a wide margin to steep open slopes at the middle and upper elevations, regardless of whether you see signs of wind-loading. Excellent riding conditions can be found at the Pass outside of wind-effected terrain.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Small wind slabs were triggered by skiers near Snoqualmie Pass in steep and complex terrain on Tuesday. This is bullseye data that wind slab avalanches will be possible on Wednesday, especially in big terrain. We expect some modest additional slab development overnight through the morning hours with a quick pulse of snow and wind. Though we don't expect large avalanches, a slab could entrain additional soft snow as it runs. Wind slabs are most sensitive when they are freshly formed and typically need a few days without active loading to heal. Keep in mind that slabs that formed in unusual locations on Tuesday could get buried by softer snow, making them more challenging to identify. 

    Check for slab and snow depth frequently and expect this problem to be more sensitive at higher elevations and anywhere you find a deeper drift. Use up-track tests, hand pits, and jump on safe and representative test slopes to help gauge slab behavior. Entrances to chutes, sidewalls of gullies, below cliff bands, and under sharp ridges are all prime locations for slab formation. Steep and unsupported open slopes are especially suspect. The safest bet is to seek out the deep fresh snow away from wind-exposed terrain where you are more likely to trigger an avalanche.

    (12/31/2024)

    Unexpected wind drifting found in localized terrain features on Tuesday. These locations below cliff bands are prime locations for wind slabs.

    Photo: Dallas Glass

Avalanche Discussion

What a difference a few days makes! The Pass has received over 6.4" of snow water equivalent since Christmas day. This has amounted to 5 feet of new snow at the Alpental Summit and almost 3 feet at the base! There are approximately 1 to 2 feet of snow over the 12/28 interface, which you should be able to identify if you dig down to it. We continue to expect any instabilities to at or above this interface.

All that new snow has done wonders to improve travel conditions. It also has led to avalanches, both natural (a few days ago) and human-triggered (on Tuesday), with a catch, carry, and partial burial reported in fairly complex terrain. Thankfully, there were no reported injuries. Though weather station wind speeds were low, NWAC forecasters and avalanche professionals found active wind loading on a normally sheltered slope on Tuesday. The wind was refilling their skin track and this red flag (active loading) caused them to dial back their objective. This is a great example of how localized winds can impact the avalanche conditions in the mountains, regardless of the free air wind speed and direction. The general reports from Tuesday were that instabilities were confined to wind-loaded slopes, and especially so in more complex terrain and on unsupported features. Snow quality and riding conditions were generally excellent and it looks like winter at the Pass. In addition, professionals reported the need to be heads up with their travel and assessment due to the prodigious quantity of recent snowfall. Open-entrance tree wells are becoming abundant and warrant some caution.

Though the precipitation totals with this next system aren’t too impressive, there are copious amounts of snow available for transport. Even modest winds can prove very effective at building wind slabs, especially when the surface snow is light and fluffy, as it currently is at the middle and upper elevations of the Pass. These lighter winds can build soft slabs, which present a good news/bad news scenario. Soft slabs tend to break at your feet and have limited ability to propagate widely across the terrain. That's the good news. The bad news is they are easier to trigger and harder to identify. While avalanche size and propagation width are important, any avalanche in complex terrain can prove dangerous.

Happy new year and enjoy all this new snow safely!

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