Lawinenlagebericht

Central Sierra Nevada

Sierra Avalanche Center
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Lawinengefahr

Sat
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Kernpunkte

Lingering storm slab avalanches could be triggered in both wind exposed and wind protected areas today.  Potential also continues for triggering large to very large avalanches failing on buried weak snow at the base of all the recent storm snow.  Dangerous avalanche conditions exist-consider avoiding avalanche terrain and run out zones below avalanche paths.

Lawinenprobleme

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–3

    Our multi-day storm that began Sunday night winded down last evening.  Lingering storm slab instabilities will continue today in both wind exposed and wind protected areas.  Large to very large avalanches failing on weak snow at the base of all the recent storm snow remains a major concern.  Consider avoiding avalanche terrain and areas below avalanche run out zones.

    Lingering storm slab instabilities will continue in wind exposed and wind protected areas.  Slabs of wind drifted snow that have formed during the storm could still be reactive today below ridges, in gully features, and on open slopes.  Large cornices have formed along ridges during the storm and will remain fragile.  Storm slab avalanches could continue to be triggered in wind protected areas on a graupel layer that was observed yesterday.  Colder temperatures have slowed settlement rates and stabilization of the storm snow.  Wet snow could begin to develop on the most sun exposed lower elevation slopes today.    

    The Feb. 10 facet layer exists on NW-N-NE aspects in wind protected terrain above around 7500'.  The avalanche accident that occurred on Tuesday is suspected to have involved this weak layer.  Whumpfing and unstable snowpack test results were recently reported indicating that this weak layer could still be reactive.  See observer video here:  https://photos.app.goo.gl/nimKWgtn4onF4pe88  Avalanches involving this weak layer would be large to very large in size, could break wider than expected running long distances, and could be triggered mid-slope or below.

         

Avalanche Discussion

The avalanche that occurred on Tuesday February 17 at the Frog Lake/Castle Peak area is a major blow to our community and the human toll is immeasurable.  Our condolences go out to all that have been affected by this tragedy.  

We have an avalanche observation here:  Perry Peak near Frog Lake/Castle Peak  We will update this page as more information becomes available.   

Weak sugary snow (near-surface facets) formed on many NW-N-NE aspects during the recent, extended dry spell in January. This weak layer was buried by new snow starting on Feb 10, and is now under 3 to 7+ feet of recent storm snow. Most areas have a thin rain crust along the top of this facet layer up to 8,600 to 8,800 ft.  This weak layer still represents a concern with uncertainty surrounding the ease of triggering large avalanches.  Weak layers, similar to the Feb 10 facet layer, have contributed to large avalanches and avalanche fatalities within our forecast area in the past.

Lower elevation areas and sun-exposed slopes experienced significant snowmelt in late January and early February, exposing areas of dirt, rock, and downed trees.  These hazards and obstacles now lie hidden, covered by low density new snow. This creates a hazard situation similar to early season coverage in some areas.  Additionally, deep open holes, open creeks, and ponded water are widespread in low-lying areas, especially below 8,000'. 

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