Lawinenlagebericht

East Slopes Central

Northwest Avalanche Center
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Lawinengefahr

Sat
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

You could still trigger a large avalanche where stiff snow overlies a soft, sugary layer near the ground, but these areas are becoming fewer and far between for now. You could also find shallow wind slabs with snow new and old. If you experience loud collapses or cracking, choose lower angle and more supported terrain.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–1.5

    As the next system approaches on Friday, watch for actively blowing snow. Slabs could be especially touchy if they are freshly forming and rest over a layer of surface hoar. Check for cracking in wind affected snow. Look for signs of drifting such as lightly bouncing snow, cornices, and textured surfaces. Steer around obviously loaded portions of very steep slopes.

    The underlying consequences of triggering even a small or shallow wind slab are that it could step down and slide on the ground. This could turn a small and fairly harmless avalanche into a large and dangerous avalanche one.

    (12/7/2022)

    Top loaded lee feature in Owl Creek. This slope would be suspect for triggering a wind slab avalanche

    Photo: Matt Primomo

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1.5–2

    The most likely area to trigger one of these surprising avalanches would be on steep northerly aspects where wind has drifted stiffer snow into a slab, and it rests over weak sugary facets. Dig down and look to identify any soft, sugary layers near the base of the snowpack (near the ground). Then all you need is a slab on top, a steep slope, and a trigger. So, in areas where you find this weak snowpack structure, conservative terrain choices and lower-angled routes are good habits. If you experience whumphing collapses, then choose lower angled terrain.

    We suspect areas near Mission Ridge and Blewett Pass have increased chances of triggering persistent slab, because the snowpack is shallow and weak in that area.

    (12/7/2022)

    A sled triggered avalanche on a road cut. On a larger feature, a bigger avalanche could have resulted. N at 6,200ft in Owl Creek.

    Photo: Matt Primomo

Avalanche Discussion

Much of the zone received 2-4" of new snow on Thursday, covering up a mixed bag of older snow surfaces. This ranged from suncrust on steep southerly aspects, to stiff wind board or soft snow. Surface hoar was fairly widespread and reported by numerous observers prior to this snowfall. Moving ahead it'll be worth quick hand pits or shovel tilt tests to try and identify if this layer is buried and preserved. The storm forecast for Friday night into Saturday should produce enhanced upslope snowfall for much of the East Central. We expect avalanche danger to become dangerous on Saturday with this storm. This storm might amount to enough snow to stress weak layers both new and old.

While access to higher elevations has improved significantly, it still requires lengthy approaches with many trees, shrubs, and stumps to avoid. Therefore, we are just beginning to understand the distribution and reactivity of these weak layers surrounding the 11/22 and 11/25 crusts throughout the zone, and we still have quite a lot of uncertainty. Evidence continues to roll in as avalanche professionals, and winter recreationists report finding this snowpack structure in many locations. However, some areas don't have enough snow overlaying this weak layer to produce avalanches. 

If you are out and about in the mountains, you can help us by submitting an observation. 

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