Lawinenlagebericht

Eastside Region

Eastern Sierra Avalanche Center
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Lawinengefahr

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

Kernpunkte

After another poor freeze overnight, a warming trend will continue to thaw the snowpack today. The combination of prolonged warming and buried weak layers is a good reason to avoid steep terrain and the runouts of large avalanche paths. As the snow surface thaws, lower slope angles with deep, uniform snow cover and no overhead hazards will be a safer bet.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1.5–3

    You could trigger a persistent slab avalanche from a distance, from flatter terrain adjacent to, or below steep slopes. A relatively small wet loose avalanche could step down to persistent weak layers at the bottom of the snowpack. Above about 10,000 feet, the snowpack has not yet adjusted to above-freezing temperatures. Persistent slabs often propagate long distances, connecting terrain features that typically contain surface instabilities such as wet loose avalanches. Where weak layers are buried more than three feet below the snow surface, signs of instability - like shooting cracks and collapsing - may be less obvious, though the possibility of human-triggered avalanches still exists. Cautious route selection remains the most important strategy to manage this problem. Choosing travel routes with lower slope angles and no overhead hazard is a good way to limit your exposure to these types of avalanches.

    (1/26/2024)

    A large persistent slab avalanche at 11,000' on the Mammoth Crest likely ran on 1/24.

    Photo: Everett Phillips

  • Loose Wet

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

    Warm air temperatures and cloud cover caused melting at the snow surface below 11,000' on most aspects over the past 48 hours. Strong inversions caused a poor refreeze above about 9,500 feet last night, and rising temperatures mean that wet snow instability is a concern today. Rollerballs and wet surface snow on steep slopes are signs that wet loose avalanches are becoming likely. Rocky chutes, vegetated slopes, and areas with shallow snow cover will be the most concerning. Shallow rocky slopes are also areas with the persistent slab problem and even a small wet sluff could be enough to kick off a much more dangerous slab avalanche involving the full depth of the snowpack. The best strategy is to avoid traveling in terrain traps under steep, snow-covered slopes as the surface thaws.

    (1/27/2024)

    Natural D1.5 wet loose avalanche in southeast couloir of Dunderberg,  Virginia Lakes.

    Photo: Clancy Nelson

Avalanche Discussion

Recent Avalanches: Wind loading on Wednesday, 1/24, resulted in multiple large to very large slab avalanches involving drifted snow and deeper persistent weak layers. These released naturally in north and northeast-facing alpine terrain between Convict Creek and Tioga Pass. Over the past 48 hours, warming and cloud cover have caused wet loose avalanche activity on easterly aspects between 9,500 and 11,000 feet. 

Snowpack Discussion: On most aspects and at all elevations, a layer of depth hoar and basal facets is buried between 2 and 3.5 feet below the snow surface under a strong mid-pack slab. Signs of instability have become less obvious where basal weak layers are buried more than 3 feet deep. However, variations in snow depth between drainages and across slopes continue to make the likelihood of persistent slab avalanches difficult to assess. The snow surface has thawed at all elevations with only a weak to moderate re-freeze overnight. Near treeline elevations and mid-slope terrain have the most significant overlap when it comes to buried weak layers and prolonged warming.

Actual air temperatures were 5 to 15 degrees warmer than forecast yesterday. Nighttime inversions have been strong over the past 48 hours. Weather stations above about 9,500 feet near and north of Mammoth have not dipped below freezing in that time. Clouds have thinned or cleared allowing the surface to refreeze here and there. The snow should melt quickly again today as temperatures climb even higher and freezing levels reach almost 12,000 feet. Warming will change the snowpack structure at all elevations. Below 9500 feet, the basal weak layers have been exposed to warm-ups earlier this season. Above 10,000 feet, persistent weak layers have not previously adjusted to above-freezing temperatures and are experiencing warming for the first time. 

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