Eastern Sierra Avalanche Forecast - 4/20/14

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THIS AVALANCHE ADVISORY EXPIRED ON April 21, 2014 @ 7:02 am
Avalanche Advisory published on April 20, 2014 @ 7:02 am
Issued by Sue Burak - Inyo National Forest
bottom line

The avalanche danger will rise from LOW this morning to MODERATE on all steep slopes 35 degrees or greater above 10,000 ft. in the Tioga, Mammoth and Rock Creek areas. Daytime warming and sunshine will melt through the overnight refreeze holding the snowpack together. Human triggered loose wet avalanches will become possible later today. Natural wet loose snow slides are possible this afternoon. 

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 will rise from LOW this morning to MODERATE on all steep slopes 35 degrees or greater above 10,000 ft. in the Tioga, Mammoth and Rock Creek areas. Daytime warming and sunshine will melt through the overnight refreeze holding the snowpack together. Human triggered loose wet avalanches will become possible later today. Natural wet loose snow slides are possible this afternoon. 

  • Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Loose Wet
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small
  • Trend ?
    Increasing Danger

Partly cloudy skies last night prevented night time lows from reaching the freezing point. Light to breezy winds also helped to keep the snow surface cooler a little longer. Strong sun and warm temperatures will melt through the thin freeze earlier than yesterday. Even though there have been only a few wet loose snow and point release slides, there is still the possiblity of human triggered loose wet avalanches today. If you see roller balls, pinwheels and point release avalanches, it is a clear sign the snow has become unstable and it's time to leave. The best way to avoid the slush is to get an early start and get off the snow by noon or early afternoon. 

Avalanche Problem 2: Persistent Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small
  • Trend ?
    Decreasing Danger

Rock Creek's weak shallow snowpack is melting off below 10,500 ft. Above 11,000 ft., there appears to be more snow than last year and depth hoar is buried under 5 to 7 ft of snow. As spring sunshine gets stronger and longer days give the sun more time to melt snow at the highest elevations, the buried depth hoar may become a stability problem or it may round and become stronger. In either case, it is a good idea to know if the layer exists under the slopes you plan to ski. Take precautions- one person at a time, avoid thin places on either sides of gullies and around rocks. 

recent observations

Yesterday, overnight lows were colder and the snow was supportable until around noon on E to SE aspects in the False White and Mammoth Lakes basin above 10,000 to 10,500 ft. Steep north facing slopes above Hammill Lake that are shaded part of the day, held moist winter snow. There was a recent wet loose avalanche that started in the rocks below. East facing slopes above Conness Lakes were slushy by 1PM. The same party reported breaking through in the meadows along Lee Vining Creek in late afternoon.  

                                                                                                                              Afternoon slush, old loose snow ava debris, Conness area

                                                              

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 39 deg. F.
Max. temperature in the last 24 hours: 50 deg. F.
Average wind direction during the last 24 hours: wsw
Average wind speed during the last 24 hours: 20 mph
Maximum wind gust in the last 24 hours: 30 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 22 inches
weather

 High pressure remains overheard with above normal temperatures today and light winds. Winds will increase tomorrow ahead of a low pressure system that will push a strong cold front through the area on Tuesday resulting in much cooler temperatures and breezy winds. High temperatures will cool about 20 degrees on Tuesday. Another system will bring cool temperatures and possible precipitation at the end of the week.  

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: mostly sunny partly cloudy windy
Temperatures: 54 deg. F. 34 deg. F. 52 deg. F.
Wind direction: SW SW SW
Wind speed: 5-10 5 10-15
Expected snowfall: 0 in. 0 in. t in.
Over 10,000 ft.
  Sunday Sunday Night Monday
Weather: mostly sunny partly cloudy windy
Temperatures: 50 deg. F. 32 deg. F. 50 deg. F.
Wind direction: SW W SW
Wind speed: 5-10 5-10 15-25
Expected snowfall: 0 in. 0 in. t in.
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