Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
1 · Low
Treeline
1 · Low
Below
1 · Low
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Out of date — this forecast expired 9 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

LOW avalanche danger exists at all elevations, but LOW danger does not mean no danger. An isolated persistent slab avalanche problem may still linger in a few areas. In the unlikely event that an isolated human-triggered persistent slab avalanche does occur, it could be large with significant consequences.

Avalanche problems

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2

    Triggering a persistent slab avalanche has become unlikely in most areas. However, recent unstable snowpit tests indicate that persistent slabs are not impossible on some isolated near and below treeline NW-N-NE aspects sheltered from previous NE winds. If a person could find just the right spot on one of these isolated slopes to trigger one of these difficult to trigger (stubborn) persistent slabs, the resulting avalanche could be large (up to D2 or D3) and destructive. Which isolated slopes may still hold a persistent slab avalanche problem is subject to significant uncertainty and variability with no clear explanation for the variations in stability across similar terrain.

    Due to the uncertainty, variability, and potential high consequences of this difficult to trigger (low probability) avalanche problem, avoiding terrain where persistent slabs may exist still represents a prudent choice. Collapsing and whumpfing, unstable snowpit test results, and handpits/probing into the snowpack to feel for a loose layer of weak snow under firm slab layers can help identify where persistent slab problems may still exist. This persistent slab problem is more likely in the mid to lower portions of the slope than at the traditional starting zone near the top of a slope.

Avalanche Discussion

* Since the last storm some snowpit tests on some near and below treeline NW-N-NE aspects in the Mt. Rose backcountry, the Carson Pass area, and the Donner Pass area have indicated that while a persistent slab may be difficult to trigger if the weak layer does break the fracture could still travel through it. Other tests from these places and other areas around the forecast area did not reveal any signs of instability associated with the persistent weak layer and snowpit tests indicated a well-consolidated snowpack.

* Ski cuts yesterday afternoon on a small E and NE facing wind-loaded test slopes on Andesite Peak produced some minor cracking but no wind slab failures. 

* Snowpit observations from Andesite Peak revealed a layer of buried surface hoar under the new snow in sheltered areas.

* A mix of rain and snow occurred up to at least 8200 ft. in some areas yesterday, leaving a thin rain crust on the snow surface.

Regions covered