Eastern Sierra Avalanche Forecast - 3/7/14

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THIS AVALANCHE ADVISORY EXPIRED ON March 8, 2014 @ 7:05 am
Avalanche Advisory published on March 7, 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. Yesterdays’ strong gusty winds blew snow onto many different aspects in alpine terrain. Look for sensitive drifts in steep north through east facing terrain and watch for small wind drifts and fresh wind slabs and evaluate the new/old snow surface. Even though the danger rating is LOW, small avalanches can occur in isolated areas on slopes steeper than 35 degrees. The avalanche danger is LOW at mid-elevations in the trees. 

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. Yesterdays’ strong gusty winds blew snow onto many different aspects in alpine terrain. Look for sensitive drifts in steep north through east facing terrain and watch for small wind drifts and fresh wind slabs and evaluate the new/old snow surface. Even though the danger rating is LOW, small avalanches can occur in isolated areas on slopes steeper than 35 degrees. The avalanche danger is LOW at mid-elevations in the trees. 

  • 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

Estimating where wind drifts and wind slabs might form used to be a lot easier- the only available wind speed and wind direction data was recorded at the top of Mammoth. Now wind speed and direction are available from the gondola towers and the top of June Mountain. Yesterday, winds raged from the west southwest at the top of Mammoth, while north winds were recorded at the upper Gondola towers. The summit of June Mountain had generally south to southwest winds.

Visual observations of snow banners swirling a thousand feet above high ridgetops complete the wind loading picture- expect areas of wind drifts and wind slabs in unexpected places on steep exposed slopes in alpine terrain. With only an inch or two of new snow blown around, the slabs and wind drifts will be small but likely sensitive to triggering. These isolated drifts vary over short distances. 

Avalanche Problem 2: Persistent 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 that continue to react in snowpack tests. 

Avalanche Problem 3: Loose Wet
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small
  • Trend ?
    Increasing Danger

As clear sunny days return, expect strong solar heating on east and south east slopes at mid elevations. Colder nights and solid refreezing on mid elevation snow will limit wet snow activity to isolated areas around rocks and cliff bands on steep slopes. 

recent observations

Observers reporting from the Mammoth Basin and June Mountain areas on Wednesday and Thursday noted no recent avalanche activity. Compression tests and extended column tests suggest the snow is becoming much less likely to produce an avalanche. Yesterday, an observer reported strong gusty winds and many cornices forming along the top of the Mammoth Crest and in the Jaws area. An extended column test on a 38 degree north facing slope below Red Cone produced a fracture but no propagation. Photo credit, Ryan Floyd. 

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 18 deg. F.
Max. temperature in the last 24 hours: 34 deg. F.
Average wind direction during the last 24 hours: WSW
Average wind speed during the last 24 hours: 50 mph
Maximum wind gust in the last 24 hours: 80 mph
New snowfall in the last 24 hours: 1-2 inches
Total snow depth: 65 inches
weather

Expect two days of sun and cooler temperatures before a weak storms move through the area on Sunday and Monday. Temperatures fell 10 to 15 degrees yesterday- highs at 9,000 ft. reached the mid 30’s after many warm days with highs reacing the upper 40's and low 50's above 9,000 ft. Over the next 5 days or more, night time temperatures will be 8 to 10 degrees colder than the first part of the week with nights reaching the low 20’s.

Winds will be from the north until Saturday night when a weak storm moves through the area bringing chances of snow to the mid and high elevations through the first part 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: Sunny clear sunny
Temperatures: 38 deg. F. 18 deg. F. 41 deg. F.
Wind direction: NE NE SW
Wind speed: 15-20 10-15 10-15
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Friday Friday Night Saturday
Weather: sun clear sun
Temperatures: 32 deg. F. 15 deg. F. 34 deg. F.
Wind direction: N N SW
Wind speed: 15-20 15-20 10-15
Expected snowfall: 0 in. 0 in. 0 in.
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