Lawinenlagebericht

Eastside Region

Eastern Sierra Avalanche Center
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Lawinengefahr

Fri
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Kernpunkte

Though natural avalanches are less likely today, the size potential for a difficult-to-predict problem is concerning. It’s possible that you could trigger a relatively small wind slab avalanche, or that a cornice could fail onto the slope above you, triggering a slide that breaks across terrain features and runs to the valley floor. Simple, sheltered terrain without that kind of overhead hazard is the safest way to travel in the mountains.

Lawinenprobleme

  • Deep Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2.5–4

    A persistent weak layer of faceted snow was buried in late February. Many deep slab avalanches released on this layer in the past 48 hours during and after a powerful storm when the weak snowpack structure was rapidly loaded by intense snowfall and wind. Don’t expect this extremely dangerous problem to stabilize as quickly as surface avalanche problems. Potential deep slab triggers may include other avalanches or cornice fall. This is particularly notable as the March sun fully hits ridgelines for the first time since the storm. Deep Slabs can propagate widely, connecting multiple start zones and terrain features. With good coverage in the tracks of avalanche paths at all elevations, some of these avalanches have reached far down into runouts and impacted areas like mature forests and flat terrain. Deep slab release is hard to predict and the problem is difficult to assess and manage. Features of concern include shallow trigger points, steep complex terrain, convexities, and slopes with overhead hazards. Uncertainty is high and avalanches could be unsurvivable. Avoidance is the best way to manage the hazard. 

    (3/15/2023)

    Nevahbe Ridge deep slab avalanche

     

     

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1.5–2.5

    Extreme southwest winds built cohesive layers of wind-deposited snow across leeward slopes through early yesterday morning. Touchy cornices developed atop ridgelines. Last night, high-elevation winds were steady from the northeast. Today you’ll find drifts ranging in size and sensitivity. Older drifts on northerly slopes will be larger, and more widespread, but more stubborn. Newer slabs on southwest slopes will be smaller, and more isolated, but may be more reactive. Use caution where the surface is rippled and rounded, and where hollow-feeling drifts sit below ridgelines and on the sidewalls of chutes. A triggered wind slab or cornice fall could step down to deeper weak layers resulting in a much larger avalanche. Sheltered terrain is a safer alternative with softer snow. 

    (3/7/2023)

    Intentionally triggered wind slab

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    The strong March sun will hit solar aspects and ridgetops today. With dry new snow above about 9000 feet, wet loose avalanches will be possible. Watch for rollerballs and small sluffs on sunny slopes as the first sign that wet loose avalanches are becoming a hazard. Rocky chutes, vegetated slopes, and areas with shallow snow cover will be the most concerning, especially if temperatures rise above freezing in your area. Plan your day to be off of and out from under very steep sunny slopes if the surface snow thaws causing you to sink into deep wet snow. 

    (2/11/2023)

    Small wet loose avalanches in steep rocky terrain triggered old wind slabs. 

Avalanche Discussion

The sheer amount of avalanche activity reported in the past 48 hours is staggering. From the Mammoth area to the north of June, size 1 to 2.5 soft slab and wet loose avalanches ran during the storm. Explosives triggered mostly size 2 wind and storm slabs yesterday morning. Some broke widely and ran far down slope.  Very large and historic avalanches breaking on deeply buried layers of old faceted snow ran down to valley floors entraining tons of wet debris below the rain line. You can look around the mountains and see the crowns and carnage. Most recent deep slabs failed between 7800 and 11000 feet on southeast, east, and northerly aspects from south of Bishop to Convict, and then again from Lee Vining north. We have one report from south of the forecast area where the observer watched a size 4 avalanche destroy a mature swath of forest yesterday, 3/15.

Keep in mind that this recent run of high-intensity storms has had serious impacts on communities, infrastructure, and road crews. Considerate travel choices and strategic parking will be appreciated if you decide to venture out today. With such good coverage at lower elevations this winter, recent avalanches have been running further, impacting roadways and buildings in the communities of Virginia lakes, Mono City, June Lake, and Aspendell. It is important to practice good run-out awareness. Triggering an avalanche above infrastructure could have devastating consequences.  Have a backup plan, remember that it often takes multiple passes to clear roadways and trailhead parking. Road crews are working overtime to allow access to communities that have recently been stranded by heavy snow, avalanche activity, and flood damage. Blocking snow drifts, travel routes, and snow piles makes it impossible for road crews to finish the job. As you walk around mountain towns with dense snow piled on rooftops, be aware that roofalanches are possible as temperatures climb.  

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