Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
View on map

Avalanche danger

Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
Open full map
Out of date — this forecast expired 8 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Avalanche danger will quickly be on the rise as this winter storm intensifies and snow levels begin to drop throughout the day.   Considerable avalanche danger will exist today and throughout the night at all elevations.  Loose wet avalanches will be likely due to high elevation rain today.  Wind slab and storm slab avalanche problems will become likely this afternoon as the storm increases and snow levels drop.  Dangerous avalanche conditions will exist with human and natural triggered avalanches expected.

Avalanche problems

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1

    Loose wet avalanches will be likely on all aspects in near treeline and below treeline terrain due to high elevation rain. Remote sensors this morning were showing rain along the Sierra Crest and Mt. Rose up to 8500-9000'.  Snow levels could fluctuate today before dropping later this afternoon.  Most instabilities should be in the form of roller balls and pinwheels but some loose wet avalanches could be larger and big enough to injure or bury a backcountry user.  As temperatures cool and the snow level drops later today, loose wet instabilities will decrease.

    Look for roller balls and pinwheels for signs of instabilities.  Avoid deep, unsupportable wet snow on steep slopes.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    Wind slabs could develop in high elevation terrain above 8500-9000' where new snow is accumulating this morning.  As the storm intensifies later today and snow levels drop, wind slabs will become more widespread on W-NW-N-NE-E-SE aspects in near treeline and above treeline terrain.  Gale force S-SW winds are forecasted throughout today and into Wednesday.

    Look for blowing snow, cornice formation, and wind pillows.  Avoid steep wind loaded areas and run out zones below wind loaded areas. 

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Storm slabs could develop later today as snow levels drop, snowfall accumulates, and snowfall intensity increases.  These storm slabs will be possible on all aspects in near treeline and below treeline terrain.  

    Look for signs of cracking and/or cohesion of the new storm snow.  Avoid steep terrain with signs of unstable snow.

Avalanche Discussion

* Warm temperatures with mostly light winds observed throughout the forecast area over the last couple days.  Minor loose wet activity reported.  Wet surface snow on north aspects by mid day up to 8000'.  Weak to no overnight refreeze of the snowpack in many areas.

* Other observations over the past week from around the forecast area targeting the recent deep slab problem have overall shown signs of increasing stability. Outliers continue to present, most recently from the Luther Pass and Echo Summit areas. General trends in snowpit data are that the once faceted weak layer of concern is located 3 to 6 feet deep in the snowpack on NW-N-NE-ENE aspects, remains significantly less dense than the slab above it, and often presents as loose grains. Varying degrees of rounding of the once faceted snow have be observed. In some locations, faceted crystals are no longer visible under magnification. In other locations, striated faceted crystals remain.  Snowpack tests mostly indicate that it is difficult to trigger weak layer failure (ECT, CT). There are some exceptions. Tests specifically examining propagation potential (such as the PST) tend to indicate that propagation could still occur along the weak layer in the unlikely event that snowpack failure is triggered.

Regions covered