Lawinenlagebericht

West Slopes South

Northwest Avalanche Center
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Lawinengefahr

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

Kernpunkte

Buried weak snow could result in high-consequence avalanches on large open slopes. The snowpack may not give you any feedback until the avalanche strikes, so your best bet is avoidance by choosing simple terrain. New snow problems still exist throughout the zone and may present as slabs or loose slides.

Lawinenprobleme

  • Persistent Slabs

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

    Don't ignore the well-documented poor snowpack structure throughout our zone. Rather, use it to drive your terrain selection on Saturday. Below the light and fluffy snow, buried weak layers 2-3 feet down consistently produce poor snowpack results, particularly on shaded aspects. The big question mark revolves around the likelihood of triggering. This problem likely won't give you any feedback that a slope is unstable until it releases. The only way to get any information about it is to dig down and take a look for yourself. Even then, your test results are only one piece of the puzzle and may not apply to nearby slopes. So what can you do? The best choice is to avoid large open terrain where triggering one of these slides would have devastating consequences. Instead of gambling, stick to small low-angle or treed slopes.

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Above our weak interfaces is plenty of recent storm snow that you may need to manage on slopes over 35 degrees. We’re wrapping this into a wind slab problem since wind-loaded slopes will be the most likely location to trigger an avalanche large enough to call consequential. With such low-density snow, blowing it around into shallow piles near ridgelines or the base of cliffs doesn't require much wind. Look for actively blowing snow, fresh cornices, or large pillow-like drifts to help identify wind-loaded features to avoid. You’ll know if you hit a wind-affected area because the snow should be stiffer than the light and fluffy found elsewhere. 

    In sheltered terrain, you may see loose avalanches running in the surface snow. Most of these should be small enough to call inconsequential but don't get caught off guard near a terrain trap.

    (2/7/2025)

    A shallow wind slab just below ridgeline in the Crystal Mountain area.

    The textured surface and relative stiffness compared to the surrounding low-density snow are easy ways to identify wind-loaded features.

    Photo: Josh Lipkowitz

Avalanche Discussion

We are a week out from the big storm that changed our snowpack and the avalanche potential in our zone. For those of you who aren't tuned in daily, we have had at least one persistent slab avalanche or whumpfing collapse reported every day since the storm except Thursday. Reports have come from Mount Adams, White Pass, Paradise, and Crystal Mountain. On Friday, NWAC forecasters in the Crystal area got two whumpfing collapses (SW 6000' and W 6000') along the ridge between East and Norse Peaks. That's a steady trickle of information that helps supplement our snowpack tests and is screaming to us all that the snowpack is not happy. 

The troublesome layers are the January Drought Layer (JDL) and the 1/10 complex. The setup will look a little different depending on where you look, but generally speaking, the JDL sits below a thin melt-freeze crust and consists of ~5cm of faceted snow over the more robust 1/10 complex. This weak structure is anywhere from 2-3 feet below the surface. Test results continue to suggest that these layers can propagate a fracture given the right trigger, including propagation saw tests repeatedly failing with cut lengths around 35 cm [PST35 END]. Just across the border in the East South zone, NWAC forecasters in the Union Basin/Gold Hill area got propagating test results on the JDL on Friday [ECTP17]. These layers aren't going away anytime soon.

So what can you do about it? Well, not much. The structure is there and well-documented. We have been getting consistent feedback with those whumpfs and avalanches. That may not always be the case, however. Conditions may "feel safe" as you travel in the beautiful new snow. But now you're too smart to be fooled by that trick. You know the poor structure trumps snowpack tests or lack of whumpfing. Avoidance is the only solution. So, don't roll out your typical playbook and terrain selections. Please keep it simple and try to fight the inviting new snow on slopes you know are potentially dangerous.

Above the persistent issues, the snowpack is generally right-side-up with a few interstorm layers and subtle melt-freeze crusts. NWAC forecasters reported shallow wind slabs near ridgelines and actively blowing snow on Friday. White Pass Pro Patrol reported the same. More snow and some wind are on the way for Saturday, particularly further south in the zone. You should manage the upper snowpack like typical post-storm snow on slopes over 35 degrees. Just remember what's below it.

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