Lawinenlagebericht

Snoqualmie Pass

Northwest Avalanche Center
Auf der Karte ansehen

Lawinengefahr

Sat
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist 3 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

With the abundance of new snow and strong winds, it's possible to trigger an avalanche on any steep slope, but be especially wary of steep terrain with deep wind drifts. Smaller avalanches may step down to deeply buried weak layers, becoming very large. Stick to low-angle slopes in simple terrain to avoid triggering a dangerous avalanche. You should also prepare for bitterly cold temperatures on Friday.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    2–2.5

    Reactive wind slabs were widespread on Thursday, and you could still easily trigger one of these avalanches on Friday. While wind slabs at mid and upper elevations have the most potential for sensitive, large avalanches, we can't rule out storm slab avalanches in steep, sheltered terrain. Smaller wind and storm slab avalanches have the potential to step down to more deeply buried weak layers, becoming very large avalanches. Friday is a day to seek out low-angle slopes to avoid triggering a dangerous avalanche. Use visual clues such as drifts and textured surfaces to identify and avoid steep wind-loaded slopes. You can also use quick hand pits or steep miniature test slopes to observe the reactivity of the new storm snow. Avalanches are likely if the snow cracks out in front of you or slides easily.

    (1/11/2024)

    The small test slope in this photo produced a mini avalanche, indicating unstable snow. 

    Photo: Andy Harrington

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3

    There is potential to trigger a very large persistent slab avalanche on deeply buried weak layers in the snowpack. These avalanches could wrap around terrain features and may even be triggered remotely from adjacent slopes or lower-angle terrain below steep open slopes. We have a lot of uncertainty around the distribution and sensitivity of these avalanches, but triggering one would likely result in an unsurvivable avalanche, so it's best to travel with wide safety margins. Avoid steep open terrain and slopes connected to steep terrain above. Instead, choose simple terrain on low-angle slopes. Alpental Ski Patrol triggered a very large (D3) avalanche during control work that failed on weak, faceted snow over the Solstice Crust. This avalanche was 2-3ft deep and took the entirety of the storm snow. It even stepped down below a more shallowly buried melt-freeze crust. In addition to this surprising avalanche, many surrounding forecast areas have had large avalanches and remotely triggered avalanches on these layers, including West South and East Central. While you may be more likely to trigger a storm or wind slab on Friday, smaller avalanches may step down to these deeper layers and become very large. 

    (1/10/2024)

    This very large avalanche released remotely from nearby explosive placement during avalanche control at Alpental. It is an indication that deeply buried weak layers could still be active. 

    Photo: Alpental Ski Patrol

Avalanche Discussion

Brrrr...be prepared for temperatures near and below 0F on Friday. Cold injuries can happen quickly, so bring extra layers, hand warmers, face masks, and make sure those grip heaters are working.  The sun should make an appearance tomorrow, and while it will likely be too cold for wet loose avalanches, you could see some sun-triggered dry loose avalanches in steep terrain.

Thursday was stormy at Snoqualmie Pass, with heavy snow and strong winds. Observers noted widespread sensitive storm and wind slabs. We have limited information from upper elevations, but at lower elevations, an NWAC forecaster found 30-40cm of snow over a crust formed during a brief warm-up on Monday night. The new storm snow was layered and reactive in both formal and informal stability tests. They also noted loose snow avalanches running with high precipitation rates of graupel.

Since the storm began on Monday afternoon, over 4.5" of water, 3-4ft of snow, have fallen in the Snoqualmie Pass area. The backcountry landscape looks significantly different than just a few days ago. Both the snowpack and our information on conditions need time to adjust to this new landscape. With this increased uncertainty, avoid stepping out into bigger terrain too quickly. Enjoy the significantly better snow conditions on lower-angle slopes as you gather more information on the state of the snowpack. We still have uncertainty regarding several weak layers in the upper snowpack (Jan 4, Jan 2, 12/25, and Solstice Crust) that contain crust/facet combinations. However, the very large (D3) avalanche triggered by Alpental Ski Patrol during avalanche control is critical information that these deeply buried layers may still be active. Snowpack test results are still producing unstable test results on the Solstice crust, which is now buried 3-4ft deep. In other zones, these layers have proven to be an ongoing problem. This is enough evidence to suggest any one of these weak layers could produce very large avalanches. 

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