Eastern Sierra Avalanche Forecast - 3/27/14

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THIS AVALANCHE ADVISORY EXPIRED ON March 28, 2014 @ 7:05 am
Avalanche Advisory published on March 27, 2014 @ 7:05 am
Issued by Sue Burak - Inyo National Forest
bottom line

The avalanche danger rating has increased to MODERATE along leeward ridgelines in alpine terrain. Watch for obvious signs of loading such as cornices, rounded drifts and rippled texture of the snow surface.  Avoiding slopes where these signs are present will be a simple way to stay out of trouble. Human triggered avalanches are possible today in steep, high elevation wind loaded terrain. 

How to read the advisory


  • Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Bottom Line

The avalanche danger rating has increased to MODERATE along leeward ridgelines in alpine terrain. Watch for obvious signs of loading such as cornices, rounded drifts and rippled texture of the snow surface.  Avoiding slopes where these signs are present will be a simple way to stay out of trouble. Human triggered avalanches are possible today in steep, high elevation wind loaded terrain. 

  • Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
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Watch for wind slabs near ridgetops following strong SW winds yesterday. This problem is simple because we can see and avoid it- thick rounded pillows of snow are easy to spot. Slabs could be dense or soft depending on the degree of wind loading. There may be slopes that missed wind loading because ridgetop winds don't always hit all slopes equally. On these slopes, watch for new snow sluffs.  

Avalanche Problem 2: Persistent Slab
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Deep buried depth hoar is widespread in the Rock Creek area on north facing slopes.This layer continues to produce sudden collapse failures on depth hoar as recently as yesterday during the storm.

advisory discussion

 Late season snow is a welcome sight and there is more on the way. The Mammoth and June Mountain areas  have picked up 10-16 inches of new snow and the avalanche problem is straightforward- small human triggered wind slab avalanches are possible today. 

A more difficult problem in the Rock Creek area is depth hoar buried at the bottom of a 3 to 4 ft snowpack. No recent avalanche activity has occurred but with easier access to high elevation terrain, there could be more potential triggers testing slopes for the just right combination of a thin area on the slope, slope steepness and the strength of the weak snow on the ground. The odds of triggering an avalanche on depth hoar are low but the consequences could be high. Avoid north facing slopes where slope angles are around 35 degrees or higher and avoid areas around rocks where the snow could be thin. 

 

recent observations

Ski patrol on June Mountain reported sluffs running with ski cuts. There was not much wind to disturb 16 inches of dry new snow. Dry new snow and no results on extended column tests were reported from the Sherwins. 

Storm snow was unstable in tests done in the Rock Creek area with consistent ECTP7-9's on the old /new snow boundary. 

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 23 deg. F.
Max. temperature in the last 24 hours: 26 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: 70 mph
New snowfall in the last 24 hours: 10 inches
Total snow depth: 44 inches
weather

Snowfall started early yesterdy morning and by the end of the day, 10 to 16 inches of snow accumulated in the June, Mammoth and Rock Creek areas. The top of Mammoth Mountain was quite windy with winds out of the southwest gusting to 70 mph. 

Periods of heavy precipitation are forecast to start Friday evening in northern California and reaching our area by  Saturday morning. The NWS writes that "This storm does have an "atmospheric river" like moisture tap with it so snow levels will start off near 7000 feet. Expect another 8-12 inches or more of snow above 9,000 ft. 

Gusty winds will precede Saturday's storm and ridgetop winds will be in the usual 80-100 mph range. A colder storm will reach the area Monday afternoon or night. It's nice to see winter return. 

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 cloudy partly sunny
Temperatures: 31 deg. F. 22 deg. F. 40 deg. F.
Wind direction: SW SW SW
Wind speed: 25 15-25 15
Expected snowfall: 1 in. 0 in. 0 in.
Over 10,000 ft.
  Thursday Thursday Night Friday
Weather: snow cloudy sunny
Temperatures: 30 deg. F. 22 deg. F. 37 deg. F.
Wind direction: W SW SW
Wind speed: 25-30 20-25 20
Expected snowfall: 1-2 in. 0 in. 0 in.
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