Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

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Limite del bosco
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Non aggiornato — questo bollettino è scaduto 9 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

CONSIDERABLE avalanche danger exists at all elevations due to a combination of loose wet, wind slab, and persistent slab avalanche problems. Intentionally choose terrain, evaluate slope aspect(s) for the presence or absence of avalanche problems, identify likely areas of triggering, and evaluate avalanche consequences in terms of potential size and down slope hazards. Determine how much you really know based on actual data vs what is a guess or pre-bias. If in doubt, make a more conservative choice.

Problemi valanghivi

  • Loose Wet

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

    Loose wet avalanche activity was occurred the past two days. Rain and wet snow will keep this avalanche problem ongoing today. In some areas below 8,500' the upper snowpack may be soaked. Snow covered NW-N-NE aspects at any elevation are the likely location for this avalanche problem to occur. Loose wet avalanches are possible in isolated areas on all other aspects as well. Avalanche size up to D2 is possible.

    Avoid steep terrain in areas where natural or human triggered roller ball activity is occurring. Even small loose wet avalanches can have significant consequences if a person is pushed into a rock or tree, over a cliff, or into a terrain trap.

  • Wind Slabs

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

    New wind slabs will have formed overnight above 8,500' in near treeline and above treeline terrain on NW-N-NE-E aspects. Isolated wind slabs may exist on cross loaded SE aspects as well. Avalanche size could reach D2. Look for and avoid areas of recently drifted snow, especially along ridgelines were signs of recent cornice and wind pillow formations exist.

  • Deep Persistent Slabs

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

    Significant rain and wet snow have added more load to areas of slab over weak faceted snow on NW-N-NE aspects both above and below treeline. Field observations from Dec 25th through yesterday have regularly indicated isolated areas of persistent slab instability. Increasing moisture in the upper snowpack from rain and wet snow have improved the strength of the facet layer in some areas. In areas where overlying slab is thicker as well as in upper elevation areas, the facets have remained drier, looser (more sugary), and weaker. Avalanches failing within the old snow up to size D2 are possible.

    Near and below treeline, quick hand pits remain effective for identifying slab over weak, loose grain (sugary) faceted snow but you may need to dig fairly deep above 8,500'. Keep in mind that this problem exists in isolated areas so investigate the snowpack structure frequently as you cover terrain. This problem may exist only in the mid to lower portion of avalanche start zones, not at the very top where past NE wind scouring occurred. Dig in the right places.

    Avoid steeper slopes in areas where snow surface cracking, whumpfing, and/or unstable snowpit test results are occurring. Keep this avalanche problem at the forefront of decision making even though it is third on the list.

Avalanche Discussion

* More loose wet avalanche activity was observed yesterday. This time it was on N to NE aspects of Red Lake Peak above Crater Lake in the 8,800' to 9,300' elevation range.

* The recent rain, wet snow, and high humidity has added significant moisture to areas that held faceted snow on the surface with no overlying slab.

* Where faceted snow exists under a slab, the facets remained dry and reactive in snowpit tests as of Friday afternoon.

* NW-N-NE aspects above 8,000' in the Mt. Rose area and along the Sierra Crest north of Emerald Bay hold the best snow coverage at 2 to 3+ feet. Overall less snow cover exists south of Emerald Bay. Areas of decent coverage exists above 8,500' on NW-N-NE aspects in the Carson Pass area.  Coverage decreases on all other aspects. Large areas of bare ground exist on the vast majority of southerly aspects at all elevations.

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