Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Several days of stormy weather and recent avalanches all point toward dangerous avalanche conditions within the zone. You might think that the snow is light and fluffy everywhere, but you could still trigger a slab on steep convex slopes, especially if they are wind-loaded. If you see cracking of the snow surface or encounter stiffer pockets of snow, avoid slopes over 35 degrees.

Problemi valanghivi

  • Wind Slabs

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

    If you’re going to trigger a slab avalanche on Saturday, it will likely be in wind-effected terrain. With plenty of low-density snow available for transport, new shallow slabs may be forming throughout the day or you could still encounter lingering slabs from earlier on in the storm. Increasing winds on Saturday should have an easterly component to them, meaning you could see some atypical loading patterns including slabs forming on different aspects or slopes being more cross-loaded than you are used to. Use visual clues such as blowing snow, textured surfaces, new cornices, or drifts behind objects to determine wind-loaded aspects. Once you know which way the wind was blowing, look for smooth “pillow-like” piles of snow that appear “fat” or feel stiffer compared to the surrounding snow to identify Wind Slabs. Using small test slopes or uptrack tests as you travel can give you clues about how wind-drifted snow is reacting to your weight as a traveler. As you ascend in elevation, you’ll likely need to manage Wind Slabs on more specific terrain features such as confined gullies and convex rollovers. As you reach the alpine, the distribution may expand to more open slopes over 35 degrees where the possibility of triggering an avalanche increases.

    (3/3/2023)

    A skier triggered slab in the Alpental Valley on 3/3 that failed on a layer of graupel. This slab stepped down to the deeper 2/25 interface.

    Photo: Aaron Richards

  • Loose Dry

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

    In more wind-sheltered areas, plenty of low-density snow is available to produce avalanches in steep terrain. Some of these avalanches may technically fail as soft slabs but behave more loose since the recent storm snow is light and fluffy. If you find a pocket that has more cohesion, be aware that slab avalanches are still possible. Regardless of how you want to categorize them, they will be easier to trigger on steep slopes over 35 degrees and could grow in size as they move downhill and fan out. You should consider avoiding large open slopes at upper elevations until the snowpack has more time to settle. Sometimes referred to as “sluffs”, don’t become complacent and be tripped up by one of these avalanches near terrain traps or in extreme terrain. 

    (3/3/2023)

    A natural small loose dry avalanche in very steep terrain. [E, 3800ft, L-N-D1-R1-S]

    Photo: Dallas Glass

Avalanche Discussion

The storm appears to be winding down but isn’t over yet for Snoqualmie Pass. As of Friday evening, the Pass has received 1.5-2 feet of new snow since Thursday (3/2 interface). This is on top of the 1.5 feet received earlier in the week (2/25 interface). Both storms were generally cold and delivered light fluffy snow. We should be able to squeeze out another couple of inches before dawn breaks on Saturday. All that to say, it’s getting pretty deep out there and you’ll have to manage new snow problems if you head into the mountains this weekend. 

The winds were significant during the early part of the storm and Alpental Pro Patrol reported triggering multiple Wind Slab avalanches up to a foot deep on Thursday morning. Any similar slabs in the backcountry likely got buried as more light and fluffy snow fell on the zone Thursday night. The early part of the storm also produced multiple periods of graupel that you may be able to find buried roughly a foot below the surface. On Friday, avalanche professionals in the Alpental Valley triggered a small slide on this graupel which then stepped down to the 2/25 interface, resulting in a large (D2) avalanche. They also reported seeing multiple natural avalanches on unsupported steep north-facing slopes above cliffs. Additional slab avalanches were reported via public observation on Humpback Mountain on the western side of the Pass proper. NWAC forecasters were on Cave Ridge and reported low-density snow lacking much cohesion, but were able to find subtle interstorm layers and signs of wind effect near ridgelines.

On Wednesday, skies cleared between our two big snow producers, and widespread weak surface hoar was reported. The sun also made an appearance, resulting in a thin sun crust on slopes that see direct sunshine. We do not have any reports of these surfaces coming into play for avalanche activity since being buried, but you should be aware of them as you perform your slope scale assessments. You could find that a poor bond exists. We expect the majority of avalanche activity to occur above the 3/2 interface but as today’s bullseye information shows us, slides could fail as deeply as the 2/25 given the right trigger and the right piece of terrain.

Regioni coperte