Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

Mon
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

If you are taking your new toys out to play in the mountains on Sunday, be prepared for cold temperatures and lots of light fluffy snow. Avalanches will be more likely in wind-loaded terrain or on slopes steeper than 35 degrees. Keep your partners in sight and don’t linger in areas where loose snow can fall on you from above. 

Problemi valanghivi

  • Wind Slabs

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

    Actively blowing snow, textured surfaces, big drifts, and wind lips were all observed at Snoqualmie Pass on Christmas Day in the near treeline band. These visual clues helped to identify wind-loaded areas and the newly formed shallow Wind Slabs where you are more likely to trigger an avalanche. As winds calm and more snow falls, these visual clues and newly formed slabs may become hidden from view on Sunday. You should take the time to feel for a change in snow depth or firmer snow below the surface as an indication that you are in wind-loaded terrain. Identifying the predominant wind direction by looking for freshly formed cornices or drifting behind natural features can give you clues as to the aspects where you need to take extra care. Wind Slabs like to form on the lee sides of ridges, near the base of cliffs, on the sides of gullies, and in confined rocky chutes. At upper elevations, slabs could be large enough to bury or kill you. If you suspect a slope to be wind-loaded, best to give it a wide berth and choose an alternate path.

    (12/23/2021)

    A small skier triggered soft slab on a wind-loaded convexity.  SW, 4800', SS-AS-R1-D1-S

    Photo: Robert Hahn

  • Storm Slabs

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

    There have been multiple reports of shallow Storm Slabs around Snoqualmie Pass the past few days. These slabs have been soft and many propagated only a short distance, but they have been able to entrain additional soft snow as they descended. Many of the reported avalanches had similar characteristics to Loose Dry avalanches, and you could find it difficult to discern between the two. Regardless of what you want to call them, the take-home point is that there is a lot of storm snow and you should be prepared to manage loose snow moving downhill on slopes over 35 degrees. You can use test slopes as a good indicator of slab potential and how the soft snow may react to your weight. Using uptrack tests or quick hand pits to look for cracking or blocks of snow failing can also give you an indication that the snow has slab properties.

    (12/24/2021)

    Shallow slabs such as this intentionally triggered slab on 12/24 show that although the snow is predominantly light and fluffy, there are areas holding some cohesion. 

    Photo: Robin Pendery

Avalanche Discussion

Over 3 feet of snow has fallen at Snoqualmie Pass proper since it started snowing on 12/22. The recent storm snow was found to be a bit denser on Saturday than it was on Friday, but it has remained relatively unconsolidated. As noted above, evidence of wind transport was also easy to spot on Saturday in the near treeline band in the Alpental Valley. Professionals found the Solstice Crust over 3 feet below the surface and a 2-inch layer of weak snow (graupel) close to 2 feet below the surface. We expect most avalanche activity to occur in the storm snow above the Solstice Crust and you need to keep your eye on the snow to see if a stiffer slab is developing. If so, the graupel layer could come into play and large avalanches could become more widespread. Additionally, a storm layer 15 inches (40cm) below the surface was repeatably producing failures during tests for at least one professional on Saturday, but no avalanches have been reported on this layer. There could be multiple layers like this in the recent storm snow, so take a look for yourself in the area where you are recreating.

On Sunday, the temperatures are expected to plummet to colder than normal. Lower elevation hikes could have more snow or ice than usual so be prepared for winter travel no matter where you are recreating. With so much light and fluffy snow, falling and not being able to get up is a real hazard. Give tree wells a wide berth, keep your partner in sight, and learn more about snow immersion hazard here.

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