Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 11 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Pockets of Moderate avalanche danger exist on all aspects above treeline and on NW-N-NE aspects near treeline and below treeline.  Low danger exists for all other areas.  Avalanche problems for today consist of wind slabs and persistent slabs.  In isolated areas, human triggered avalanches are possible today.  Evaluate snow and terrain carefully, identify features of concern.

Avalanche problems

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Persistent slab avalanche problems are still a lingering concern in isolated terrain for today.  The surface hoar that was buried on 12/13 and caused human and natural triggered avalanches is still being found on N-NE aspects near treeline and below treeline in wind protected but open terrain.  Yesterday the surface hoar that was found was mainly not reactive to snowpack tests and hand pits and appeared to have collapsed from the weight of the new snow above.  There have been no reports of additional avalanches associated with this weak layer since Sunday but there still could be pockets were this layer is still reactive. 

    The 12/10 and 12/13 rain crust both formed early in the last 2 storm cycles as warm storms approached then quickly turned to cold snow.  Developing near crust facets on both these layers could pose a persistent weak layer for now and into the future.  These problems have been seen in the Carson Pass/Ebbetts Pass/Bear Valley area on NW-N-NE aspects 8000' to 9000'.  In the Carson Pass area yesterday, snowpack tests were showing that both these layers were reactive.  The 12/13 layer is down about 1' and the 12/10 layer is down around 2.5' from surface.  In other areas this weak layer has not been seen.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Ongoing NE winds in the moderate to strong range will continue to scour the above treeline N-NE-E aspects and move snow onto the SE-S-SW-W-NW aspects today  Wind slabs will continue to develop on these aspects with pockets of wind slabs found in complex terrain on all aspects above treeline.  Recent below average cold temperatures will slow the bonding process of these wind slabs and have them linger through today.  Look for blowing snow, snow surface scouring, cornice formation, and well defined wind pillows for clues as to where wind slabs may occur.

Avalanche Discussion

Recent observations throughout the forecast area have shown that the 12/13 buried surface hoar layer is limited to specific areas and limited in reactivity.  Most of this surface hoar was thought to be destroyed by wind, sun and rain before it could be buried by new snow.  At Blue Lakes (Carson Pass Area) and at Powderhouse Peak (Luther Pass Area) the buried surface hoar layer was not found.  At Hidden Peak (West Shore) it was found in protected open areas but not reactive and thought to have collapsed under the weight of the new snow.

Moderate to strong NE winds were redistributing existing snow and creating small sensitive wind slabs that were reactive to a skiers' weight on all aspects above treeline.  This was observed on Hidden Peak (West Shore) and blowing snow was seen near and above treeline in the Carson Pass and Mt. Rose areas.

Developing near crust facets have been observed at the 12/10 and 12/13 rain crusts.  These facets are becoming reactive to snowpack tests and have mostly been limited to the southern half of the forecast region (Carson Pass, Ebbetts Pass/Bear Valley 8000-9000'.)  No other signs of instability have been associated with these layers.

 

 

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