Bollettino valanghe

Eastside Region

Eastern Sierra Avalanche Center
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Pericolo valanghe

Mon
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Use extra caution on steep slopes with wind-stiffened surface snow. Watch for blowing snow and rounded, textured drifts that crack around you. When in doubt, limiting your exposure to wind-affected terrain is a safer option. Frigid temperatures and poor coverage increase the consequences of getting caught in an avalanche.

Problemi valanghivi

  • Wind Slabs

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

    Strong southwest winds at all elevations blew snow onto leeward slopes yesterday. Winds have shifted east and north at higher elevations, moving snow onto southerly aspects. Use caution around sensitive drifts downwind of ridgelines and the sidewalls of cross-loaded gullies. Slabs could be larger near the Sierra Crest, and in drainages that received more new snow. You may find drifts further down the slope than expected, and downwind of tight trees. Watch for blowing snow and growing cornices that point to the freshest drifts on southerly slopes. Hard slabs from last night may be less obvious. You'll find them on the northern half of the compass. They can break from the edges and propagate across the slope. Shooting cracks and the sound of the snowpack collapsing under your weight are warning signs that wind slabs are unstable in your area. Remember that even a relatively small wind slab avalanche breaking in the upper snowpack may be enough to step down to persistent weak layers, creating a larger avalanche.

    (1/6/2024)

    Gale force winds moving snow in the Sherwins.  

  • Persistent Slabs

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

    Observations over the past week have highlighted faceting throughout the entire snowpack, limiting the areas where a slab rests over weak snow. Newly drifted snow may have stiffened slabs over sugary layers found throughout the fragile early-season snowpack. Approach steep terrain with wind-stiffened snow cautiously. Shooting cracks or whumpfing noises from the snowpack are signs that you’ve wandered onto an isolated slope where the persistent slab problem is still active. If triggered, the resulting avalanche could break in unexpected ways - from across the slope, or from below. Shallow snow cover may increase the likelihood of collisions with rocks and trees in the runout. 

    (12/28/2023) Photo: Steve Mace

Avalanche Discussion

A cold and windy winter storm cleared the region quickly overnight. Snow totals in the Eastern Sierra this morning are less than were forecasted, with higher totals near the Sierra Crest. Extreme southwest winds that accompanied the heaviest snowfall have shifted east and will shift again to the north today.

Shifting winds have been a theme over the past week. A storm on the 3rd deposited fresh slabs on northerly slopes when several natural, human, and explosive-triggered avalanches were reported across the Mammoth area. Friday, extreme northerly winds stripped snow cover from many ridgetops, taking them back down to rock and dirt.

The shallow snowpack on shady slopes has been weak and faceted since November. Storms in early and mid-December buried exceptionally weak depth hoar which is still sitting at the base of the snowpack. That overlying snow faceted as well during cold dry spells. These weak grains are layered around decaying melt-freeze crusts and old thin wind boards. The January 3rd storm again buried faceted crusts under loose, low-density snow. Where winds have compacted recent snow near the surface, thin slabs could collapse the fragile underlying structure.  

Coverage across the forecast area has been limited this season. The Mammoth area has had the most consistent snow. Very cold wind chills and the chances of injury from hitting rocks and logs could turn an avalanche accident into an unpleasant rescue scenario today.

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