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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Highlights

MODERATE avalanche danger will continue today due to loose wet and deep slab avalanche problems.  Loose wet avalanche activity will be possible at all elevations as rapid warming occurs and rain becomes possible this afternoon.  Deep slab avalanches remain possible in isolated areas of the forecast region.  Avalanche danger is expected to increase over the next few days as a larger storm impacts our area.

Avalanche problems

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Loose wet avalanche activity is expected to increase today with rapid warming and rising snow levels.  Wet instabilities will be possible on all aspects and elevations today.  Rain is expected up to 7500' by this afternoon and up to 8000' by this evening.  Most loose wet instabilities should be in the form of roller balls or pinwheels but some larger loose wet avalanches are possible and could be large enough to injure or bury a backcountry user-size D2.

    Monitor the weather and snow surface conditions in your area today.  Thick, wet surface snow may occur with rapid warming and/or rain on snow later today.  Look for roller balls and other signs that the snow surface is loosing strength.  Avoid travel on steep slopes where roller balls are occurring.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    2 natural and 1 human triggered deep slab avalanches have been reported in the Mt. Rose area post storm.  On Sunday, the most recent, a group of backcountry users remotely triggered a deep slab avalanche in the Mt. Houghton area.  After further investigation, a layer of graupel that fell on Tuesday before our last big storm is sitting on top of a melt freeze crust and below the recent storm snow.  This graupel/melt freeze crust combo is now buried 3 to 5' deep.  All 3 of these deep slab avalanches have been on East aspects, above 9000', and in the Mt. Rose area.  Snowpack tests done yesterday at the crown of a recent deep slab avalanche still show that this layer is reactive and that propagation continues to be likely.

    Many unknowns still exist about this deep slab issue.  The only effective management strategy is avoidance-staying off aspects of concern, using slopes under 30 degrees on aspects of concern and avoiding connected terrain where remote triggering could occur.  Any avalanches associated with this weak layer would be large and have severe consequences. 

Avalanche Discussion

* A deep slab avalanche with a crown height estimated at 4 feet was remotely skier triggered Sunday on Mt. Houghton on an E to ENE aspect at approx 10,200'. The party triggered a large collapse just below the ridgetop. Investigation down slope revealed the avalanche crown below a cliff band.

* A crown line profile was done on a recent deep slab avalanche SE of Relay Peak.  The weak layer was a layer of graupel on top of the melt freeze crust that is below the recent storm snow.  This graupel/melt freeze combo seems to only exist above 9000' on aspects that had melt freeze crusts pre storm.  This layer is thought to be responsible for all 3 of the recent deep slab avalanches in the Mt. Rose area.  Snowpack tests done at the crown line showed unstable results showing propagation is still likely.

* Observations from The Nipple (Carson Pass area) showed a mostly stable snowpack.  Tests and observations focused on the old melt freeze crusts did not show any signs of instabilities.

* Other observations around the forecast region, Jobs Peak and Shirley Canyon, show some instabilities continue to exist.

 

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