Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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2 · Moderato
Limite del bosco
2 · Moderato
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In sintesi

Pesky ENE winds have left small fresh slabs of wind drifted snow near upper elevation ridgelines. Daytime warming and sunshine may also allow some loose wet avalanche problems to form on lower elevation sunny slopes. On top of these two problems, an unlikely but not impossible deep slab problem still may exist on some isolated near and below treeline slopes. MODERATE avalanche danger continues.

Problemi valanghivi

  • Wind Slabs

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

    Stronger than forecast ENE winds created fresh slabs of wind drifted snow near some upper elevation ridgelines yesterday. Since there is still some snow for transport and those ENE winds picked back up this morning small sensitive wind slabs may still exist on wind-loaded and cross-loaded SE-S-SW-W-NW-N aspects in above treeline terrain. Today's sunshine could make these wind slabs easier to trigger on sun-exposed slopes. 

    Blowing snow, smooth pillows of wind drifted snow, and fresh cornices above a slope can help identify where these wind slabs may exist.

  • Loose Wet

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

    Sunny skies and warmer daytime temperatures could create enough wet surface snow for some loose wet avalanche problems to form once the snow warms up. These issues would be less likely in areas exposed to this morning's ENE winds or in areas where cloud cover develops this afternoon. 

    Wet sticky snow, rollerballs, and pinwheels of wet snow indicate that enough warming has occurred for loose wet avalanche problems. Once you see signs of warming like this it is time to find a colder aspect, move to lower angle slopes, or head back home. 

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2

    The recent storm overloaded the weak old snow and resulted in a deep slab avalanche cycle. Observations have trickled in this week, and we can now piece together a deep slab timeline. Several large avalanches released naturally during the storm last Sunday (3/15) and maybe Monday (3/16). Once the storm ended, numerous people have been traveling in the backcountry. Despite the increased backcountry traffic, only a few human-triggered deep slabs have been reported. Some occurred on 3/17 south of the forecast area and one large avalanche occurred on 3/18 (it was not reported until 3/20). One human-triggered deep slab avalanche occurred on isolated terrain features on each of 3/19 and on 3/20. During this time snowpit data has shown a trend for these kinds of avalanches becoming more difficult to trigger.

    Most evidence indicates that triggering a deep slab avalanche has become unlikely on a regional scale. That being said, some uncertainty still exists surrounding this problem and it may not be impossible. In the unlikely event that one of these does occur it would be on an isolated terrain feature on a NW-N-NE aspect in near or below treeline terrain where the weak layer exists.  

    Due to the consequences of an unlikely but not impossible deep slab avalanche and some degree of uncertainty around this problem, it still warrants consideration. If you have any doubts about the potential for a deep slab, go ahead choose a different aspect or more conservative terrain.

Avalanche Discussion

Observers reported 3 small wind slabs near the ridge of the Bronco Chutes on Relay Peak yesterday (more details here). Stronger than forecast E winds created these reactive wind slabs. Another avalanche was reported in Powderhouse Bowl that caught a person. No injuries were reported. No additional details about the avalanche were reported. 

Snowpit tests and other observations from near a deep slab avalanche on Martis Peak that likely occurred on Wednesday 3/18 indicated that triggering that avalanche would be more difficult yesterday but that if the weak layer started to break the resulting fracture might still propagate through that weak layer. 

Snowmobilers reported some rollerballs and pinwheels during the afternoon on sun-exposed slopes around 6000 ft near Wrights Lake.

 

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