Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

Don't be fooled by the danger rating. If you trigger a slab avalanche today it could be ugly and occur on a slope that already has many tracks on it. MODERATE avalanche danger exists at all elevations with persistent slab and loose wet avalanche problems.

Problemi valanghivi

  • Deep Persistent Slabs

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

    A skier triggered avalanche with persistent slab characteristics was reported yesterday on a slope with many previous tracks and it had wide propagation. Snowpit data from other areas and avalanches from Sunday are creating the picture of the possibility of continued persistent slab avalanches failing on barely faceted snow just below the crust at the old/new snow interface. So far this instability has been observed on N-NE-E aspects ranging from 6,800' to 10,100'. NW-N-NE-E aspects at all elevations are the main areas of concern. Avalanche size is expected at D2 with up to D3 possible.  Any avalanche of this type would involve all of the snow from this last storm, failing 1 to 3+ feet deep. Anticipate the possibility of additional avalanches occurring today on slopes with previous tracks and breaking wider than expected.

    MODERATE danger persistent slabs are a difficult to manage low likelihood, high consequence situation if you choose to travel the slopes where they may lurk. The easy choices for managing this hazard are to simply say no thank you by choosing SE-S-SW-W aspects for avoidance or by entrenching on sub 30 degree slopes without steeper terrain above or to the side. Your compass and inclinometer are handy tools.

      Photo: Yesterday's avalanche on Relay Peak with many previous tracks and wide propagation.

  • Loose Wet

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

    Warming today and periods of sunshine and solar radiation through and between the cloud cover will allow the strong April sunshine to create snow surface warming on all aspects. This surface warming and melt will allow for the possibility of loose wet avalanches today on all aspects. Avalanche size is expected at D1 to D2 depending on what the terrain is capable of producing.

    Roller balls and pinwheels are indications of the presence of this avalanche problem. Consequences from even small loose wet avalanches can come from being pushed into or over rocks, trees, cliffs, and terrain traps below. Lower angle slopes can be used to avoid this avalanche problem.

     Photo: Loose wet avalanches yesterday on NE aspect of Flagpole Peak (Echo Summit area).

Avalanche Discussion

* A skier triggered avalanche with persistent slab behavior occurred yesterday afternoon on Relay Peak (Mount Rose area). This avalanche had wide propagation and there were many previous tracks on and adjacent to this slope when the avalanche was triggered. This avalanche likely failed on the underside of crust at the old/new snow interface. The avalanche occurred on an E aspect at about 10,100' in above treeline terrain.

* Snowpit data collected yesterday a short distance to the SW of Relay Pk on a NE aspect at 9,640' in near treeline terrain showed similar instability on barely faceted snow crystals on the underside of the crust at the old/new snow interface.

* Snowpit data and an intentional skier triggered avalanche reported Sunday on Tressle Peak (Donner Summit area) described a similar weak layer at 6,800' on E to NE aspect terrain.

* Loose wet avalanches occurred yesterday on Flagpole Peak (Echo Summit area) on steep open NE aspect terrain below 7,600'.

* More sun than expected yesterday will have led to the overnight formation of breakable crust in many areas on all aspects.

Regioni coperte