Eastern Sierra Avalanche Forecast - 3/12/14

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THIS AVALANCHE ADVISORY EXPIRED ON March 13, 2014 @ 7:05 am
Avalanche Advisory published on March 12, 2014 @ 7:05 am
Issued by Sue Burak - Inyo National Forest
bottom line

The overall avalanche danger is generally LOW for the Mammoth Basin and June Mountain areas.  Even though the danger rating is LOW, small avalanches can occur in isolated areas on slopes steeper than 35 degrees. Isolated areas of small wind slabs may be found in alpine terrain and small wet loose snow instability may occur on east through southeast facing slopes at mid-elevations below the alpine zones.  

How to read the advisory


  • Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Bottom Line

The overall avalanche danger is generally LOW for the Mammoth Basin and June Mountain areas.  Even though the danger rating is LOW, small avalanches can occur in isolated areas on slopes steeper than 35 degrees. Isolated areas of small wind slabs may be found in alpine terrain and small wet loose snow instability may occur on east through southeast facing slopes at mid-elevations below the alpine zones.  

  • Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1: Wind Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small
  • Trend ?
    Decreasing Danger

Very small areas of wind drifted snow formed from the inch or two of new snow that fell Sunday and Monday along the Mammoth Crest. Ski tests did not produce results. In steep rocky terrain, isolated areas of small wind slabs may be foound today.  

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

After a cold morning, temperatures will slowly climb to the upper 30's and low 40's by mid day. Strong March sun will melt the snow surface at mid-elevations in the trees. Chances for loose wet snow slides increase tomorrow and will become the primary avalanche problem by Friday.   

advisory discussion

The depth hoar layer is buried under 4-5 feet of snow in the Mammoth Basin except in some north to east facing gullies that avalanched in early February. Observations in Hammil Bowl yesterday were made in on slopes where last week’s avalanches occurred. Snow depths were shallow (2-3 feet) and the snow surface was firm hard wind affected snow. There was 8-12 inches of fist hardness depth hoar at the bottom. Extended column tests did not propagate cracks.

As spring approaches, these north facing slopes receive longer periods of direct sun and eventually the surface will melt. When liquid water reaches depth hoar and facets, there is a sudden loss of strength and wet slab avalanches may occur.

Temperatures remain cool today though solar radiation will melt the snow surface at mid-elevations in the trees. Chances are increasing for loose wet avalanche activity by Thursday.  

recent observations

Yesterday’s snowpack observations include reports of fractures propagating in extended column tests in shallow (40-60 inches) of snow on northeast facing slopes around 9,500 to 10,000 ft. on  Mammoth Mountain.  Similar propagation has been observed in Rock Creek on north aspects. This thick layer of fist hard depth hoar is still capable of propagating a crack. What this means is high elevation, shaded north facing slopes that held snow beginning in October, November and December up and down the eastern Sierra probably harbor this potential weak layer.  Even during LOW danger ratings, normal caution and mountaineering savvy includes probing to determine the thickness and extent of the layer.

The depth hoar layer is buried under 4-5 feet of snow in the Mammoth Basin except in some north to east facing gullies that avalanched in early February. Observations in Hammil Bowl yesterday were made in on slopes where last week’s avalanches occurred. Snow depths were shallow (2-3 feet) and the snow surface was firm hard wind affected snow. There was 8-12 inches of fist hardness depth hoar at the bottom. Extended column tests did not propagate cracks.  Air temperatures were cold in the shade- only reaching 19 degrees. 

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 17 deg. F.
Max. temperature in the last 24 hours: 40 deg. F.
Average wind direction during the last 24 hours: East
Average wind speed during the last 24 hours: 50 mph
Maximum wind gust in the last 24 hours: 82 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 50 inches
weather

After a cold night,  temperatures will reach the upper 30’s and low 40’s today but the significant warm up is forecasted to begin tomorrow and continue through the weekend. East winds blowing across the ridgetops could gust over 75 mph today.  

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Wednesday Wednesday Night Thursday
Weather: sun clear sunny
Temperatures: 34-36 deg. F. 21 deg. F. 45 deg. F.
Wind direction: NE NE NW
Wind speed: 15-25 10-15 5-10
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Wednesday Wednesday Night Thursday
Weather: windy breezy sunny
Temperatures: 33 deg. F. 22 deg. F. 41 deg. F.
Wind direction: NE NE NW
Wind speed: 20-25 15-20 10
Expected snowfall: 0 in. 0 in. 0 in.
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