Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Stronger winds may create small areas of unstable, wind-blown snow near ridges today. The larger deep avalanches keep getting harder to trigger as the old snow gains strength. However, avalanches 4 to 6+ feet deep may remain possible in some places. Using gentler terrain away from steep slopes can help avoid both these issues. 

Avalanche problems

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2.5–4

    The Dec 1 weak layer still exists underneath 4 to 6+ feet of strong snow. Triggering an avalanche that fails on this layer gets more difficult with each passing day. A large trigger might provide enough force, like a cornice collapse or multiple people on a slope. Hitting a trigger point in a shallow area of the snowpack where the weak layer is closer to the surface may also still trigger a deep slab avalanche. While the chances of triggering one of these avalanches continue to decrease, the consequences remain the same. If one of these avalanches occurs, it would be enormous and unsurvivable. 

    Weak layer depth, variability, and a lack of obvious signs of instability make assessing stability challenging with a deep slab problem. Often, triggering a catastrophic avalanche is the first and only clue that the slope is unstable. Be patient; this problem will become less of an issue soon. Recreating in sub-30 degree terrain or on SE-S-SW aspects where this problem does not exist represent two ways to avoid this problem and still get out to enjoy the snow.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    The forecast calls for stronger, more consistent NE and E winds today and tonight. These may be strong enough to scour snow surfaces and move snow onto the N-NW-W-SW-S aspects. Small slabs of wind-drifted snow could form near ridgelines.  Most of these wind slabs should remain shallow and not extend very far downslope. A few of them may grow large enough to cause problems for backcountry travelers in the most wind-exposed terrain.

    Clues like blowing snow, drifted snow, and wind-created surface textures can help identify where wind slabs may exist. 

Avalanche Discussion

  • Reports of large persistent slab avalanches that failed near the storm's end (likely Sunday) keep coming in from all over the forecast area. These deep avalanches propagated across slopes and wrapped around terrain features. We also have reports of avalanches that failed on the buried surface hoar layer during the storm. 
  • Thanks to everyone for playing it safe and being patient. If all goes well today, it will be day four without avalanche activity. Also, thanks to everyone who has sent in observations. Please submit an observation with a photo and location info if you see a large crown or any lingering signs of instability.

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