Eastern Sierra Avalanche Forecast - 3/9/14

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THIS AVALANCHE ADVISORY EXPIRED ON March 10, 2014 @ 7:05 am
Avalanche Advisory published on March 9, 2014 @ 7:05 am
Issued by Sue Burak - Inyo National Forest
bottom line

The avalanche danger is rated generally LOW for the Mammoth Basin and June Mountain areas. Intense sun and warm temperatures could produce wet loose snow avalanches today. 

How to read the advisory


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

Bottom Line

The avalanche danger is rated generally LOW for the Mammoth Basin and June Mountain areas. Intense sun and warm temperatures could produce wet loose snow avalanches today. 

  • Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1: Loose Wet
  • Character ?
  • Aspect/Elevation ?
  • Size ?
    Historic
    Very Large
    Large
    Small
  • Trend ?
    Increasing Danger

The hazard from wet snow avalanches is increasing with night time temperatures failing to produce solid overnight freezes. Today’s intense sun and warm air temperatures will increase the chances for loose wet avalanche activity. Although typically small, they can knock you down and carry you through nasty terrain.  

Avalanche Problem 2: Deep Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Trend ?
    Decreasing Danger

Deep slab avalanches are becoming more unlikely as observations of rounding depth hoar and facets remain consistent over time. There are exceptions- any steep slope where the snow cover is thin, and in Rock Creek. In Rock Creek the total snow depth is around 24 inches and 12 inches are depth hoar and facets. ECT’s done on north slopes above Rock Creek Lake showed lingering instability about 16 inches down from the snow surface.  

advisory discussion

Last winter close to this date in March, a large skier triggered avalanche occurred east of TJ Bowl in the Mammoth Basin. There was 84 inches of snow on the Mammoth Pass snow pillow. This year there is 67 inches of snow. Last year, the snow structure was weak and this year the snow structure is similar but the depth hoar layer is thicker and there are many melt freeze crusts in the Mammoth Basin snow pack than last year. This is due to the alternating periods of mild weather followed by cold with some fresh snow in between. Every crust has facets below the crust- this winter’s snowpack structure is more complex and faceted than last winter’s.

As unwelcome high pressure builds into the west coast next week, the combination of longer days and strong sun will begin another round of mid elevation snowmelt and could impact north facing slopes above tree line. Once again, the snow will go through another rapid transition and avalanche danger could increase by the end of this coming week. 

recent observations

Snowpits dug in the June Mountain area suggest the inter storm layer noted previously this week is strengthening. Many north through east facing slopes steeper than 35 degrees avalanched during last weekend's storm. 

Today along high ridge tops in the June Mountain area, old wind drifts were visible but did not react to ski tests. Snow depths were shallower than average snow depths in the Mammoth Basin (4 ft compared to ~5-6 ft.)- probably because of the widespread avalanche cycle that occurred in the Negatives and on north and east facing high elevation slopes around San Joaquin Mountain. Most avalanches ran on the old snow surface that existed prior to the Feb 28-March 2 storm.  Multiple extended column tests on northerly slopes above 10,000 ft. produced no propagation at 28 to 30 taps.  

Observers noted small wet snow slides on east to southeast facing slopes in the Mammoth Basin. A report from the Sherwin Ridge told of winter snow along the ridge and mixed stability test results on an inter storm layer about 15 inches down from the snow surface. Mid elevations were loose and unsupportable in places. 

 

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 30 deg. F.
Max. temperature in the last 24 hours: 51 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 5-10 mph
Maximum wind gust in the last 24 hours: 10 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 53 inches
weather

Temperatures climbed 10 to 15 degrees yesterday; today is off to a warm start after last night’s lows only reached 30F.  Temperatures increase this morning under mostly clear skies- later today, clouds move in and temperatures will fall. Winds will be light and from the southwest today. Yet another storm in a long dry winter passes to the north later today; snow is likely tonight and Monday with a few inches of accumulation expected above 8,500 ft.  

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Sunday Sunday Night Monday
Weather: sun cloudy rain and snow
Temperatures: 45 deg. F. 28 deg. F. 38 deg. F.
Wind direction: SW SW SW
Wind speed: 0-15 5-10 20-30
Expected snowfall: 0 in. 1 in. 1 in.
Over 10,000 ft.
  Sunday Sunday Night Monday
Weather: clouds clouds snow clouds with snow
Temperatures: 44 deg. F. 25 deg. F. 30 deg. F.
Wind direction: SW SW SW
Wind speed: 10-15 25-30 25-30
Expected snowfall: 0 in. 1 in. 1 in.
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