Eastern Sierra Avalanche Forecast - 4/4/14

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THIS AVALANCHE ADVISORY EXPIRED ON April 5, 2014 @ 7:05 am
Avalanche Advisory published on April 4, 2014 @ 7:05 am
Issued by Sue Burak - Inyo National Forest
bottom line

The avalanche danger is generally LOW today. Isolated areas of wind drifted snow and soft slabs can be found below ridgelines in steep north to east facing alpine terrain that could be sensitive to human triggering. Most of the wind slabs that formed during and after the storm have probably settled out but always be cautious on steep slopes with recent wind deposits.  Loose dry snow avalanches may still be triggered in very steep terrain in alpine areas. The avalanche danger is estimated to be LOW in mid elevation 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 is generally LOW today. Isolated areas of wind drifted snow and soft slabs can be found below ridgelines in steep north to east facing alpine terrain that could be sensitive to human triggering. Most of the wind slabs that formed during and after the storm have probably settled out but always be cautious on steep slopes with recent wind deposits.  Loose dry snow avalanches may still be triggered in very steep terrain in alpine areas. The avalanche danger is estimated to be LOW in mid elevation terrain. 

  • Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
  • Character ?
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    Very Likely
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  • Trend ?
    Decreasing Danger

The recent storm deposited 12-18" of new snow above 9500 ft. The storm was unusual for a spring storm because winds were light, temperatures were in the teens. and have remained cold for the last few days. Some wind drifting and pillows formed below the high ridges; slabs have been soft and pockety in distribution. The snow is settling and becoming more dense- this action is increasing stability but there are isolated areas below ridgelines where a skier or rider could trigger a slab avalanche.

 

Avalanche Problem 2: Deep Slab
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The snowpack is scary on steep north facing terrain above 10,000 ft.  in Rock Creek. Triggering an avalanche on the depth hoar layer is becoming harder to do- it involves hitting a trigger point on a slope. The problem is we don't know where these trigger points exist and some slopes may have many trigger points while others may have only one and others may have none at all.  This is a situation where putting one person on the slope at a time is crucial.  If you do trigger an avalanche, it could be large or small, depending on the terrain.

The photograph is the displacement of the slab when the depth hoar layer collapsed. The depth hoar layer was close to 12 inches and the displacement of the slab is about 10 inches. PST 16/200 (end) down 82 cm.

See also https://www.youtube.com/watch?v=ndPUa2ms0fY&feature=youtu.be

 

Avalanche Problem 3: Loose Dry
  • Character ?
  • Aspect/Elevation ?
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  • Size ?
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    Decreasing Danger

Human triggered loose dry snow avalanches are possible in isolated areas in steep alpine terrain today. Many slopes steeper than 35 degrees have already slid or have been triggered but the snow is cold and dry. Consider the consequences of getting pushed around by a loose snow avalanche if you above terrain traps, rocks, cliff bands and trees.

advisory discussion

Light winds, cold temperatures and 12- 16" of dry snow have made epic skiing and riding conditions throughout the forecast area. This has been one of the driest winters in many years and yet we are enjoy great skiing and riding conditions even in a drought year.

recent observations

Observers  reported propagation on an extended column test on a ENE facing slope at 11,000 in the Hammil Bowl area, ECTP 23. The weak layer was within the storm snow of early in the weak and the overlying slab was 13 inches thick.

On Tuesday, a party found a large stiff wind slab at the entrance of a steep chute in the Mammoth Basin. Ski cutting produced no results. 

Reports of easily triggered loose snow sluffs in terrain steeper than 35 degrees came from the Negatives.

In high exposed north facing terrain in the Rock Creek area, extended column tests continue to propagate on large depth hoar on the ground.

https://www.youtube.com/watch?v=ndPUa2ms0fY&feature=youtu.be

 

 

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 19 deg. F.
Max. temperature in the last 24 hours: 32 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 30 mph
Maximum wind gust in the last 24 hours: 50 mph
New snowfall in the last 24 hours: T inches
Total snow depth: 58 inches
weather

A weak storm is expected to reach our area today. Skies are clear to partly cloudy this morning with light southwest to west winds. Scattered snow showers and cold temperatures continue for one more day before the warmup begins on Saturday. 1 to 2 inches of snow are expected today at the 8,000 to  10,000 ft elevations this afternoon.  2 inches of new snow is expected above 10,000 ft with light west to northwest wind gusting to 25 mph by mid day.

Spring returns this weekend with sunny skies and temperatures climbing 15-20 degrees from today's highs. There is a possibility of another storm by the end of next week.

 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Friday Friday Night Saturday
Weather: clouds and snow showers cloudy sun
Temperatures: 24 deg. F. 18 deg. F. 32 deg. F.
Wind direction: West north North
Wind speed: 5-10 5-10 5-10
Expected snowfall: T in. T in. 0 in.
Over 10,000 ft.
  Friday Friday Night Saturday
Weather: clouds and snow clouds sun
Temperatures: 24 deg. F. 15 deg. F. 33 deg. F.
Wind direction: W W North
Wind speed: 5-15 5-15 15
Expected snowfall: T in. T in. 0 in.
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