Eastern Sierra Avalanche Forecast - 3/27/14

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THIS AVALANCHE ADVISORY EXPIRED ON March 28, 2014 @ 10:36 pm
Avalanche Advisory published on March 27, 2014 @ 10:36 pm
Issued by Sue Burak - Inyo National Forest
bottom line

The avalanche danger is MODERATE in steep alpine terrain. Wind slabs formed on Tuesday on north through east facing aspects could be sensitive to skier triggering and human triggered avalanches are possible today. Mid elevations in the trees did not received the snow fall amounts and wind loading that exposed alpine elevations did and the avalanche danger rating is estimated to be LOW. 

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 is MODERATE in steep alpine terrain. Wind slabs formed on Tuesday on north through east facing aspects could be sensitive to skier triggering and human triggered avalanches are possible today. Mid elevations in the trees did not received the snow fall amounts and wind loading that exposed alpine elevations did and the avalanche danger rating is estimated to be LOW. 

  • Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
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  • Trend ?
    Decreasing Danger

The main concern will be avalanches breaking in the new storm snow and on the old snow surface. The old snow surface is highly variable- crust and facet combinations and weak near surface facets on shady slopes, old wind board, melt freeze crusts and more. Dry storm snow fell on these old surfaces and a very limited number of stability tests showed results within the new snow and at the old snow/new snow interface. 

Avalanche Problem 2: Persistent Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small
  • Trend ?
    Same

Rock Creek has much colder snow temperatures due to a generally colder climate than the Mammoth and June Mountain areas. The combination of cooler temperatures, shaded north facing slopes and a shallow two to three foot snowpack has created continental snowpack conditions. Depth hoar at the bottom of a 2 to 3 ft. snowpack continues to produce sudden collapse failures. 

advisory discussion

There were no reports of recent avalanche activity in the backcountry yesterday. One person skied the Negatives yesterday without incident. This is not sufficient information to convince me that avalanche danger rating is LOW. Over 12 inches of new snow fell on Wednesday accompanied by strong winds during and after the storm. The lack of natural activity is worrisome because it means the wind loading and new snow was not quite enough to create avalanches during the storm, so it is possible that wind slabs in alpine terrain are still sensitive to skier triggering.  

Ski patrol reported 4-8" wind slabs releasing with ski cuts and larger slabs with hand charges. Backcountry avalanche forecasters pay attention to ski patrol control results during and after a storm because it gives relevant information on new snow instability- it is reasonable to expect that if ski cuts are producing small wind slabs in storm snow on Mammoth and June Mountains and there was no natural avalanche activity reported from the Mammoth Lakes basin, it is possible for a skier or rider to trigger an avalanche today. Avoid steep wind loaded terrain- look for rounded pillow forms below ridgetops. 

Today will be the day before the next storm and I expect this weekend storm to produce a natural avalanche cycle because of the amount of snow fall in a short period of time. 

recent observations

No natural avalanche activity was reported yesterday in the Mammoth and June Lake areas. The wind transported alot of snow along the Mammoth Crest and left it's trademark of wind ripples alternating with soft to medium hardness wind slabs. 

Control results on Mammoth Mountain yielded wind slabs up to 18" released with hand charges and smaller slabs released with ski cuts. 

An observer report from the Red Cone area showed propagation within the storm snow at 8 inches down from the surface and propagation 12 inches down at the old snow/new snow interface. Tests at mid elevations in the trees produced no results.  Photo credit: B. Wickers

 

 

 

 

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: 28 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: 1 inches
Total snow depth: 45 inches
weather

No new snow has fallen in the last 24 hours. Morning temperatures are in the upper teens and low 20's and winds are blowing from the southwest from 20-25 mph. 

A Winter Storm Watch has been posted by the National Weather Service,beginning tomorrow afternoon and ending late Saturday night or early Sunday morning.  A period of heavy snow Saturday night will drop 12 to 18" of new snow in the mountains above 8,000 ft. 

Skies will be mostly cloudy today with southwest wind winds blowing 20-25 mph. Snow begins tomorrow afternoon with the main event coming Saturday night. 12 to 18" of new snow will fall in a 6 to 8 hour period. 

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: clouds clouds snow
Temperatures: 40-48 deg. F. 21-28 deg. F. 38-46 deg. F.
Wind direction: SW SW SW
Wind speed: 25 25 55
Expected snowfall: 0 in. 0 in. 3 in.
Over 10,000 ft.
  Thursday Thursday Night Friday
Weather: clouds clouds snow
Temperatures: 33-41 deg. F. 20-26 deg. F. 31-36 deg. F.
Wind direction: SW SW SW
Wind speed: 30 35 50-75
Expected snowfall: 0 in. 0 in. 4 in.
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