Lawinenlagebericht

Stevens Pass

Northwest Avalanche Center
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Lawinengefahr

Sun
Hochgebirge
3 · Erheblich
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

Steer around fresh wind drifts on steep slopes at upper elevations. If you hit the wrong spot, you could trigger a large and surprising slab avalanche on shaded, northerly aspects. Stick to lower-angled slopes and dig to look for older weak layers of snow.

Lawinenprobleme

  • Wind Slabs

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

    The wind may drift the newly fallen snow into soft, reactive slabs. The higher you go, the more likely you may be to trigger small slab avalanches. Look for signs such as wind-blown snow and shooting cracks. Steer around drifts on leeward sides of ridges and steep rolls in the terrain.

    We have good confidence that west winds will be strong Friday night and become moderate out of the northwest and that temperatures will warm by Saturday evening. We are unsure exactly how much new snow will fall. Unfortunately, we have more than just new snow avalanche problems. You could also trigger a persistent slab avalanche.

    (12/9/2021)

    An example of wind features from earlier this season, Stevens Pass.

    Photo: Josh Hirshberg

  • Persistent Slabs

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

    There's still a chance that you could trigger a surprising slab avalanche that could break widely across a slope. Watch for "red flag" signs like whumphing collapses, cracks shooting through the snow, and tests that propagate or fail suddenly. If you see this, stick to slopes less than 35 degrees and avoid traveling in or under large avalanche paths and steep slopes. Put plenty of space between where you travel and big terrain features. 

    The late January weak layer can be found 1.5-2ft below the surface. Weak sugar-like facets (or surface hoar) sit above, and sometimes between, a crust. We have the best information that you can trigger these avalanches on NW-NE aspects between 4,000ft and 4,700ft. This low elevation band produced startling collapses and shooting cracks earlier in the week. There is uncertainty with higher elevation, alpine terrain. Continue to use caution and consider avalanche terrain on the north half of the compass guilty until proven innocent, especially in wind-loaded areas. 

    (2/1/2022)

    Very long shooting crack in a wind drifted slope on a north aspect at 4,000ft near Henry Creek. The slab failed in weak, faceted grains above a stout crust. The crack ran about 100ft long.

    Photo: Matt Primomo

Avalanche Discussion

Warm temperatures have formed thin crusts and helped snow bond. Rollerballs and moist, sticky snow were reported at lower elevations in the past 2 days. Most recently, observers have reported tests and profiles on northerly aspects at mid-elevations showing favorable bonds and rounding of the previously faceted, late-January weak layer. On Thursday, explosive testing at Stevens Pass Mountain Resort produced no results on east through south aspects from 4,800 to 5,000ft. These are all good signs regarding the persistent slab problem. Earlier in the week, observers reported shooting cracks or whumphing collapses on northerly aspects in the low 4,000ft elevation band (Stevens Pass proper, Yodelin, and Henry Creek clearcuts). Uncertainty continues with upper elevations, as we have limited information from above 5,600ft. 

In late January, near-surface facets and surface hoar were found to have survived on a variety of shaded, northerly slopes, especially below 4,700ft. Warm temperatures and mixed rain/snow on the 30th may have melted these weak layers in some areas at mid-elevations, but perhaps not all. Approach the backcountry with an assessment mindset and be ready to stick to lower-angled terrain. Check out the other recent observations from Henry Creek, Upper Nason creek, and the Stevens Pass sidecountry. Let us know what you find, and if you experience whumphing collapses or shooting cracks to better track these tricky conditions. 

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