Lawinenlagebericht

Central Sierra Nevada

Sierra Avalanche Center
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Lawinengefahr

Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

Areas of MODERATE avalanche danger exist above 8,000' both above and below treeline on slopes 35 degrees and steeper due to a combination of newly formed wind slabs above 8,000' and difficult to trigger persistent slabs above 9,000'. Below 8,000' to 9,000' firm icy surfaces exists in many areas and could pose dangerous travel conditions with long sliding falls possible.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1

    A new round of wind slabs is expected to have formed last night above 8,000' in near and above treeline areas on NW-N-NE-E-SE aspects due to the combination of new snow and wind. In the majority of areas that received just 1 to 3 inches of new snow, any new wind slabs will be small and not present a significant hazard to backcountry travelers. In the isolated areas above 9,000' that potentially received up to 7 inches of new snow last night, wind slabs could be large enough to present a significant hazard to backcountry travelers today. Look for new cornice formation, new wind pillows, and areas of human triggered snow surface cracking that point towards recent wind loading. In locations where signs of recent wind loading point to the presence of this wind slab avalanche problem, avoid slopes 35 degrees and steeper.

  • Deep Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    2

    The persistent slab avalanche problem is an ongoing issue above 9,000' on NW-N-NE aspects both above and below treeline. Likelihood of triggering is temporarily decreased today with the break between large new snow loading events on the snowpack. That said, triggering a large, destructive, difficult to survive avalanche is not impossible today, just less likely than over the past several days. The most likely scenario for a large avalanche to occur today is for a human triggered wind slab avalanche to occur on the slope first and then step down with additional snowpack failure on the deeper persistent weak layer of old faceted snow.

    Likelihood of triggering is expected to increase again Thursday-Friday as significant amounts of new snow above 9,000' drastically increase the amount of stress on the faceted weak layer. Significant amounts of new snow are also expected to transition this persistent slab avalanche problem to a deep persistent slab avalanche problem in the coming days.

Avalanche Discussion

Observations made yesterday on Tamarack Peak (Mount Rose area) and on Elephant's Back (Carson Pass area) pointed towards ongoing issues with faceted snow above 9,000' on NW-N-NE aspects. This is the weak layer associated with the ongoing persistent slab avalanche problem. Snowpit tests indicated increasing difficulty in triggering during the lull between new snow loading events stressing the snowpack. These tests also indicated that once snowpack failure is initiated, large destructive avalanche activity remains likely.

Other recent observations have shown firm icy conditions on all aspects from recent rain on snow events below 8,000' to 9,000'. Last night's rain is expected to have done little to soften this icy snow surface. The potential for long sliding falls exists in some areas.

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