Lawinenlagebericht

Central Sierra Nevada

Sierra Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist 4 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Shifting winds and new snow in the last 24 hours have left unstable slabs of snow on slopes where wind-blown snow has piled up. Adding a person on top of that wind-blown snow would likely trigger an avalanche today. Some unstable snow may also exist on steep slopes in sheltered areas, especially in places where the most new snow fell yesterday. Watch out for signs of unstable snow like recent avalanches, blowing snow, and cracking snow, and move to gentler terrain if there is any doubt about the snow's stability. 

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1.5–2.5

    Winds shifting between SW and NE have blown snow back and forth across ridges and deposited wind slabs on almost all aspects over the last few days. The back-and-forth transport has compacted the snow into more dense wind slabs in some areas. People have triggered and gone for rides in wind slab avalanches the last two days, and triggering a wind slab avalanche remains likely if people venture onto steep, wind-loaded slopes today. In addition to the wind slabs, huge cornices have also formed above many wind-loaded slopes. The largest wind slabs will exist in near and above treeline terrain, but the strong winds may have built a few on open lower-elevation slopes near ridges.

    Recent avalanches, blowing snow, cornices, drifted snow, dense hollow-sounding snow, and wind-created surface textures all indicate the presence of wind slabs. The shifting winds may make identifying which slopes have been wind-loaded more challenging. Route plans that locate and skirt around potentially unstable wind slabs can help avoid getting caught in a wind slab avalanche. This planning will also steer your group into more sheltered terrain where less wind-affected snow will likely exist.

    (1/16/2023)

    Long shooting cracks on a cross-loaded N facing slope above the standard skin track on Mt. Judah

    Photo: Andy Anderson

  • Storm Slabs

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

    More reports of storm slab instability came in yesterday, including avalanches and shooting cracks. These weaknesses typically do not last very long. Still, they could linger within the storm snow or at the boundary between storm snow layers today. Deeper storm slabs will exist in the southern part of the forecast area, where more snow fell yesterday. Triggering a storm slab avalanche while traveling on a steep slope may remain possible today. 

    Recent avalanches or shooting cracks indicate that the storm snow remains unstable. Feeling heavy snow on top of lighter snow or layers of storm snow that easily separate from the snow below them can also help identify where unstable storm slabs may linger. If any signs of instability or uncertainty about a slope exist, bypass that area and switch to sub-30-degree slopes without steeper terrain above.

    (1/16/2023)

    Storm slab instability on a small test slope near Deer Park on an NW aspect at 6800 ft.

    Photo: Alpenglow Expeditions

Avalanche Discussion

The deep snowpack has several rain crusts buried in it. Some thin layers of weak snow may (or may not) exist around some of these crusts, but they are so deeply buried (8 to 17 ft) that it is difficult to trigger them or assess them with snowpit tests. Widespread avalanche activity that fails this deep in the snowpack remains unlikely. Unlikely does not mean impossible, and an isolated deep avalanche that fails on a crust would not be out of the question. It would be impressive, but the abovementioned avalanche problems should represent most avalanche activity.

Recent Observations

  • Numerous wind slab and storm slab avalanches have occurred in the last few days. Some have involved enough snow to bury people, and some have been smaller. Along with these recent avalanches, widespread shooting cracks have also been reported.

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