Eastern Sierra Avalanche Forecast - 2/27/14

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THIS AVALANCHE ADVISORY EXPIRED ON February 28, 2014 @ 7:41 am
Avalanche Advisory published on February 27, 2014 @ 7:41 am
Issued by Sue Burak - Inyo National Forest
bottom line

The avalanche danger in the Mammoth Lakes and June Mountain areas is rated CONSIDERABLE this morning. High precipitation rates and moderate southwest and southerly winds created unstable conditions on north to east facing slopes at tree line and in alpine terrain. Today, continued snow and wind will make human triggered avalanches likely on all wind loaded slopes above treeline.  Slopes that have not received a wind load have a MODERATE avalanche danger. 

Widespread natural avalanche activity in the Negatives last night is a sure sign of dangerous avalanche conditions in wind loaded terrain today. 

How to read the advisory


  • Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

Bottom Line

The avalanche danger in the Mammoth Lakes and June Mountain areas is rated CONSIDERABLE this morning. High precipitation rates and moderate southwest and southerly winds created unstable conditions on north to east facing slopes at tree line and in alpine terrain. Today, continued snow and wind will make human triggered avalanches likely on all wind loaded slopes above treeline.  Slopes that have not received a wind load have a MODERATE avalanche danger. 

Widespread natural avalanche activity in the Negatives last night is a sure sign of dangerous avalanche conditions in wind loaded terrain today. 

  • Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Storm Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
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    Very Large
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  • Trend ?
    Increasing Danger

Wind loaded slopes are the primary avalanche concern today. Upper elevation slopes facing north to east will be the most likely to produce an avalanche. Mid elevation slopes exposed to cross loading may produce an avalanche as well- these slopes have a MODERATE danger. Even though the main snow event comes tomorrow, last night's new snow came in fast and furious with snowfall rates of 2" per hour. New snow instability spiked rapidly and it will take some time for the snow pack to adjust to the new load. 

Avalanche Problem 2: Persistent Slab
  • Character ?
  • Aspect/Elevation ?

Weak snow in the upper 6 to 8" of the old snow poses stability concerns today, The facet/crust sandwich has been reacting in stability tests, The new snow may not bond well if near surface faceting exists- winds were moderate on ridge tops  but glades and open areas in the trees may harbor weak surface snow. 

Deep buried depth hoar and facet layers near the ground will be loaded over the next two days- the question is, will there be enough snow to reactivate this layer? The Friday storm may add enough weight to overload old weak snow but it will probably be an isolated concern. 

recent observations

Observations over the last two days show widespread surface faceting and facets under crusts in the upper 6 inches of the snowpack in the Mammoth Basin. These layers received a heavy load in a short time last night. 

A natural avalanche cycle occurred in the Negatives last night- reports of widespread avalanche activity in the bowl. It is believed the storm snow slid on the old snow surface.

June Mountain ski patrol reports numerous avalanches running on the old snow/storm snow boundary.  

 

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 22 deg. F.
Max. temperature in the last 24 hours: 39 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 50 mph
Maximum wind gust in the last 24 hours: 80 mph
New snowfall in the last 24 hours: 10 inches
Total snow depth: 43 inches
weather

Light snow is falling this morning and temperatures are in the low 20's and upper teens above 9,000 ft. Snow showers continue this morning until mid day when partly cloudy skies may allow the sun to break through the cloud cover.

The next storm is on track to hit the area hard tomorrow morning and throughout the day. Two to 3 feet of snow could accumulate above 9,500 ft in the Mammoth and June Mountain areas. 

Temperatures today will reach the mid 30's at the 8,000 to 9,000 ft elevations. Strong southwest winds will impact the mid elevation with gusts to 50 mph. Another 2-4 inches could fall today. Higher terrain will pick up another few inches of snow accompanied by very strong southwest winds gusting to 70 mph. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Thursday Thursday Night Friday
Weather: snow then partly cloudy partly cloudy snow
Temperatures: 35 deg. F. 25 deg. F. 35 deg. F.
Wind direction: SW S S
Wind speed: 25-30 25-30 20-30
Expected snowfall: 2-4 in. 2 in. 18 in.
Over 10,000 ft.
  Thursday Thursday Night Friday
Weather: cloudy partly cloudy cloudy, snow
Temperatures: 25 deg. F. 20 deg. F. 29 deg. F.
Wind direction: SW SW S
Wind speed: 50-55 30-40 30-40
Expected snowfall: 2-4 in. 2 in. 20 in.
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