Eastern Sierra Avalanche Forecast - 4/24/14

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THIS AVALANCHE ADVISORY EXPIRED ON April 25, 2014 @ 10:27 pm
Avalanche Advisory published on April 24, 2014 @ 10:27 pm
Issued by Sue Burak - Inyo National Forest
bottom line

The avalanche danger rating is estimated to be LOW early this morning but will soon increase to MODERATE and possibly higher later today and tonight. Eight to 12” of new snow is forecasted to fall today and tonight along with sustained 60-80 mph west and southwest winds.  Winds are blowing 50-60 mph this morning- expect widespread areas of unstable wind slabs to form today on north facing slopes below ridgetops and on exposed leeward slopes above treeline. 

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 rating is estimated to be LOW early this morning but will soon increase to MODERATE and possibly higher later today and tonight. Eight to 12” of new snow is forecasted to fall today and tonight along with sustained 60-80 mph west and southwest winds.  Winds are blowing 50-60 mph this morning- expect widespread areas of unstable wind slabs to form today on north facing slopes below ridgetops and on exposed leeward slopes above treeline. 

  • 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
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  • Trend ?
    Increasing Danger

Wind slabs. Wind transport of snow last night combined with today’s wind and snowfall will keep the concern for unstable wind slabs going throughout the day. Alpine terrain on north through southeast aspects hold the greatest instability today.Human triggered slab avalanches are possible in alpine terrain on wind loaded slopes. Watch for rounded pillows of wind deposited snow below ridgelines- strong winds will form wind drifts well below ridgelines in the middle of slopes or around rocky sub ridges.  

 

 

 

advisory discussion

Fresh snow and colder temperatures will briefly halt the downward melting spiral of the 2014 snowpack. A foot of new snow falling at the end of April presents challenging avalanche conditions- wind slabs on north slopes and wet loose snow avalanches on sun exposed aspects will occur at the same time.

Today, cold temperatures, wind and fresh snow create wind slab avalanche problems on lee ward slopes. Small wind drifts will likely form in localized areas over icy crusts on sun exposed slopes.  By this evening, snowfall should pick up and another 8 inches could fall, bring storm totals of a foot or more. Wind loaded slopes could see drifts of over 2 feet. The wind shifts from the southwest to the northwest as the storm passes late tonight, so expect wind loading on east and south east aspects on Saturday. 

If the sun comes out at all Saturday, cold new snow will get a blast of strong solar energy that could weaken the snow surface and create loose snow avalanches of varying sizes, depending on the new snow depth, how long the sun is out, the slope aspect and slope steepness.  

Sunny weather on Sunday and slopes with spring powder will create an irresistible package, but don’t leave your brain behind. Sunday will be one of those days when everything “feels right”, but make sure you back this with some observations of wind activity, recent avalanche activity and sound decision making. Avalanches never care how you’re feeling-- they’re heartless. 

recent observations

Cool nights and mild days created pleasant spring skiing conditions in the Mammoth Basin and Tioga Pass areas over the lasts two days. Snow pits on an east aspect inthe Gaylor Peak vicinity revealed flow channels through the upper 2 ft. of a 5 ft deep snowpack and wet snow avalanches can become less frequent- but there are always exceptions. High elevation north facing slopes are still hold dry to moist winter snow. 

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 21 deg. F.
Max. temperature in the last 24 hours: 36 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: 2 inches
Total snow depth: 17 inches
weather

Strong west and southwest winds began to blow yesterday afternoon on Mammoth Mountain and at Ellery Lake. This morning, the winds are blowing 50-60 mph and wind gusts of 80 mph occurred early this morning. Snow is falling this morning with 2 inches of accumulation so far. Snow showers will continue through the morning with 3-5" of snow expected above 9,000 ft.

After mid morning, snowfall will taper until this afternoon. The main event occurs this evening with 4-8 inches expected in the mountains bringing storm totals of 7 to 14". Ridgetop winds will be very strong with gusts of 80 mph. 

Daytime highs today and Saturday will be in the mid 40's with lows in the 20's. Saturday will be unsettled with snow showers  in the morning, with gusty northwest winds. 

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: snow snow chance of snow
Temperatures: 30 deg. F. 17 deg. F. 30 deg. F.
Wind direction: SW NW W
Wind speed: 30-35 gust to 55 mph 20-25 10-20
Expected snowfall: 3-4 in. 3-5 in. 0 in.
Over 10,000 ft.
  Thursday Thursday Night Friday
Weather: snow snow chance of snow
Temperatures: 25 deg. F. 11 deg. F. 29 deg. F.
Wind direction: SW SW NW
Wind speed: 30-40 gust to 60 25-30 20-30
Expected snowfall: 3-5 in. 3-7 in. 0 in.
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