Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
4 · Forte
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

High winds, additional snow, and weak old snow surfaces create a tricky and dangerous avalanche problem. You can easily trigger large avalanches in both wind-drifted snow near ridgelines and sheltered terrain where recent snow fell on weak surfaces.  Choose conservative low-angle terrain and limit your exposure to large open slopes above. 

Problemi valanghivi

  • Storm Slabs

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

    Strong winds and plenty of new snow falling on old, weak surfaces create overlapping and variable avalanche problems. Winds will form large and sensitive wind slabs in exposed terrain at mid and upper elevations. These slabs may form lower on the slope than anticipated and even run naturally. If that wasn't enough to avoid, sensitive storm slabs may be widespread on northerly terrain, particularly in open glades and meadows where recent snow fell on weak facets and surface hoar.  With this high level of uncertainty and variability, reign in your terrain selection and enjoy the return to winter on low-angle sheltered terrain with limited overhead exposure. 

    The usual strategies and tricks you use to manage risk might not be reliable, given the variation in snowpack structure below the new snow. Some slopes might produce no avalanches or smaller slabs. On other slopes, even those adjacent, you could trigger unusual avalanches that propagate widely, release when you are in the middle of a slope, or might even be triggered from below. Be especially wary of skiing into steep open glades in northerly terrain. Even a small avalanche could push you into trees, rocks, or over cliffs. 

    (2/24/2021) An example of a widely propagating avalanche in new snow from a previous season. Rock Mtn. SE, 5,800ft.  Photo: Josh Hirshberg

Avalanche Discussion

Temperatures will plummet overnight, and showery snowfall will linger through Saturday. Depending on the convergence zone's placement, Stevens Pass can expect another 1-1.5ft of snow, with high snow-to-water ratios. Winds will be very strong, possibly with extreme gusts. The snowpack structure is unusually variable, and weak snow layers aren't likely to go away quickly. Conservative decision-making is essential. 

You can keep your decision-making simple and enjoy the fresh snow in low-angle terrain. If you choose to venture into avalanche terrain, there's a huge range of variable old snow layers to consider.  Consider avoiding steep slopes in open or gladed north-facing terrain. Snow fell on slick crusts on steep southerly terrain, and east and west aspects likely harbor an unpredictable distribution of both surfaces. As we gain more information, we'll likely be able to narrow the areas where we suspect avalanches are most likely. However, gaining confidence in the distribution takes a lot of patience and many observations.

For the past couple of weeks, we've been tracking surface conditions. On Thursday, an NWAC forecaster in the Lichtenberg and Valhalla Lake area found softening crusts on sunny slopes and large (up to 2mm) facets on the surface of shaded slopes. On the 29th, an NWAC forecaster investigated a steep, south aspect on Cowboy Ridge and found that the top three feet of the snowpack had turned to melt forms. See other observations from last weekend here and here. 

If you get out in the mountains, let us know what you see by submitting an observation HERE or via the Avy App. 

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