Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

Dangerous avalanche conditions continue to exist throughout the forecast region due to a deep slab avalanche problem at all elevations.  Large destructive avalanches have occurred in our area and continue to be possible today.  Loose wet avalanches will be likely today as daytime warming occurs.  Make a plan with your group that avoids terrain and exposure to the current avalanche problems.  Cautious route finding and conservative decision making are essential.

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    3

    More avalanche reports have come in that show that a widespread deep slab avalanche cycle has been occurring throughout the forecast area on NW-N-NE-ENE aspects at all elevations.  Many of these deep slabs occurred during or immediately after the storm and released naturally.  There have been at least 3 that have been human triggered post storm with 2 occurring on Sunday.  Deep slab avalanches continue to be an ongoing avalanche problem today.

    The issue is a layer of faceted snow that exists 4 to 8' deep below the snow surface.  This can be difficult for a backcountry user to get force down to this weak layer where it is deeply buried.  Likely trigger points could be areas where the weak layer is closer to the snow surface like near: rocks, trees, cliffs, convex rollovers, and areas with a shallower snowpack. 

    All of the deep slab avalanches that have occurred so far have had wide propagation and have been large avalanches (D3 or bigger-large enough to destroy a house and break trees up to taking out large swaths of mature forest).  Tracks on a slope will not indicate stability as was shown from Sunday's avalanche at Lost Lake (Carson Pass area) where the slope was tracked out before the avalanche was triggered.  These deep slabs have the potential to be remotely triggered as was shown by the Negro Canyon avalanche ( Donner Summit area) where the avalanche occurred 500' away from the trigger point in lower angle terrain with shooting cracks traveling up to 1000' away. 

    Deep slabs are unpredictable and signs of instability may not be present.  The only effective management option is avoidance.  Avoid slopes steeper than 30 degrees and slopes connected to steeper terrain on NW-N-NE-E aspects.  Good recreation conditions currently exist on Northerly aspects that are below 30 degrees in steepness with no steeper avalanche terrain connected. 

  • Loose Wet

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

    As daytime warming occurs today, loose wet avalanches will become likely on E-SE-S-SW-W aspects at all elevations.  Warming temperatures that are well above freezing with March levels of solar radiation will cause an increase in loose wet activity today.  Most of this activity should be in the form of roller balls and pin wheels but some larger loose wet avalanches are possible and could be large enough to injure or bury a backcountry user.

    Avoid steep sun exposed aspects when daytime warming occurs. 

Avalanche Discussion

* 3 human triggered Deep Slab avalanches have occurred over the last 4 days.  On Saturday, a skier triggered deep slab occurred on Schallenberger Ridge (Donner Summit area).  On Sunday, 2 deep slab avalanches occurred.  One in Negro Canyon (Donner Summit area) while digging a snowpit in lower angle terrain, and one at Lost Lakes (Carson Pass area) triggered by a snowmobiler.  All of these deep slab avalanches were at least D3 or above, all had wide propagation, with crowns ranging from 4 to 8' with one reported up to 15 to 20' deep in spots.

* Many more reports have come in that show a widespread Deep Slab Avalanche cycle has been occurring.  Natural avalanches from Mt. Tallac, Pole Creek, Desolation Wilderness, 2 from Trimmer Peak, and National Geographic Bowl.  In all cases these avalanches occurred on N-NE-ENE aspects and had crown heights of 4 to 8 feet plus.  See observations below for photos and other specifics.

* Warming effects have been reported throughout the forecast area on E-SE-S-SW-W aspects. 

Regioni coperte