Avalanche forecast

Eastside Region

Eastern Sierra Avalanche Center
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Avalanche danger

Tue
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

You can trigger a dangerous avalanche today where strong and shifting winds are building unstable slabs. Clearing skies and increasing temperatures may introduce wet snow instability to sun-exposed slopes.  Localized assessment of changing weather and snow conditions and patient, conservative decision-making are essential today.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2.5

    Winds have shifted from the southwest to the north over the past 24 hours but continued at high enough speeds to move snow, especially at higher elevations. There is abundant soft snow available for building new slabs and wind slabs will continue to grow in size today. The main change from yesterday is that the pattern of loading will be more complex with potentially unstable slabs around terrain features that block and redirect winds on all aspects.  Be alert for signs of instability such as shooting cracks and audible slope collapses. Large drifts, recent cornice growth, hollow upside-down feeling snow, and uneven snow surfaces are all clues that indicate nearby wind deposits. Do your own localized assessments and carefully evaluate terrain features that encourage drifting, such as the leeward sides of ridgelines, alpine couloirs, gully features, and cross-loaded depressions. 

    Large human-triggered wind slab on an E aspect near treeline yesterday. (3/31/2024)

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Wet snow avalanches will become possible as clouds and winds decrease and temperatures rise.  Although warmer today, temperatures will likely remain below freezing above treeline, limiting wet avalanche concerns to mid and lower elevations. Wet surface snow, sinking into wet snow past your boot top, or roller balls coming down from cliff bands are warning signs that loose wet avalanches are becoming a problem. Very steep, rocky slopes and areas with thin snow cover will warm first as the sun hits them. Conditions will vary with aspect and elevation across the forecast area. Localized assessments of surface thawing and deep wet snow will be key. Consider the slopes above you and plan your exit to avoid overhead hazards as the day warms.

    Small wet loose avalanche below treeine.

    Photo: Steve Mace

Avalanche Discussion

Recent avalanche activity: Over the past 48 hours multiple large natural and human-triggered wind slab avalanches occurred on north through east-facing slopes near and above the treeline.  Small storm slab avalanches were widespread below the treeline following the snowfall on 3/30/23, but no new storm slab activity was reported below the treeline yesterday.

Snowpack details: Following an extended period of clear weather from March 16th to March 22nd, up to 3 ft of new snow fell in the Eastern Sierra over the past week. This stormy period has been exceptionally cold for this time of year leading to very low-density snow that is prone to wind transport and slab building. The storm snow from the past 48 hours is denser near the snow surface (upside down) even in sheltered areas (see storm slab activity above). Around Mammoth Lakes three layers of rounds and decomposing and fragmented precipitation particles make up the upper meter of the snowpack, these increase in hardness until the strong old snow surface from 3/22 is reached. Outside of the Mammoth Lakes area, recent snowfall may be nearer 1 to 1.5 feet and it is easier to feel the old snow surface from before this storm. In mid and upper-elevation terrain prone to wind loading the low-density snow has been sculpted into a patchwork of wind slabs that have been sensitive to triggers including loose dry avalanches from above, other wind slabs, and humans. Even though it’s April, the snowpack is not yet a settled spring snowpack. Be prepared for changing conditions and be mindful of how your actions could affect travelers below you.

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