Eastern Sierra Avalanche Forecast - 4/18/14

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THIS AVALANCHE ADVISORY EXPIRED ON April 19, 2014 @ 7:03 am
Avalanche Advisory published on April 18, 2014 @ 7:03 am
Issued by Sue Burak - Inyo National Forest
bottom line

The avalanche danger is mostly Low but this morning but rises to MODERATE as snow heats up with sun and cloud cover adding additional energy from the greenhouse effect.  

It's easy to tell what's happening out there, but there is alot of variability and tsnow conditions can change rapidly. The danger rating reflects average conditions.  

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 mostly Low but this morning but rises to MODERATE as snow heats up with sun and cloud cover adding additional energy from the greenhouse effect.  

It's easy to tell what's happening out there, but there is alot of variability and tsnow conditions can change rapidly. The danger rating reflects average conditions.  

  • 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

After a thin refreeze last night, the sun will melt quickly due to warming from reflected energy from mid level clouds forecasted for today. Once the freeze melts, enough loose wet snow will exist for human triggered wet snow avalanches. Signs of surface instability includes pinwheels, roller balls and loose wet point releases will become possible on all steep aspects.  Getting out early and leaving the slopes before last night's refreeze completely melts represents a good way to avoid dealing with unsupportable wet snow. Once the refreeze does melt, skiing and riding conditions deteriorate and the avalanche hazard increases. At that point finding a different afternoon activity that does not involve steep snow covered slopes is a great idea.

 

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

Recent observations from Rock Creek show the depth hoar layer collapses without warning on flat, gentle and steep terrain.  Nights are colder with a much better refreeze than Mammoth but the snow is shallow and melt weakens the snow by mid day. The highest elevations in Rock Creek have 5-7 ft of snow in steep north facing bowls and so far, a few observations suggest the snow is supportable and in transition from dry to moist snow.  

advisory discussion

Last night, clouds kept overnight lows above freezing. Cloud cover today and tomorrow means all slope aspects will get similar amounts of energy; north slopes will receive similar amount of the sun's energy as east and south slopes. In addition, there has been a string of warm nights.  This signals a snowpack with limited refreezing and when followed by warm days (either sunny or cloudy and warm) can dramatically increase the likelihood of natural and human triggered avalanches. Careful route planning to stay out from under slopes with wet and rotten snow is essential during this period.

 

recent observations

Small point releases occurred on east and southeast aspects above treeline in the Mammoth area. Minor wet sluffs occurred on steep sun exposed slopes in the False White area near Tioga Pass. An observer wallowed in facets while booting up a gully near Tioga Pass yesterday but reported supportable conditions on the descent and along flat terrain. Spring snow along valley bottoms, higher elevations are an assortment of wet and dry rough crusts and some spring snow.  

The snow becomes unsupportable above 10,000 ft by mid morning n some areas in the Rock Creek drainage.

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: 54 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: 24 inches
weather

A cold front brushed by the area last night. This front brings in moisture/instability that could produce isolated thunderstorms over the high elevations today and tomorrow afternoon. The risk of thunderstorms doesn't sound that great, about 30%, but if a thunderstorm should develop, expect brief periods of heavy rain, lightning, and erratic winds. 

Daytime highs above 10,000 ft will reach 50 F with a 30% chance of rain and snow. Southwest winds will be light, 5-10 mph. Around thunderstorms, strong gusty winds up to 45 mph are possible. Mid-elevations reach the mid 50's to 60 F with nights in the 40's. 

 A fast moving, cold storm will impact the area Monday night into Tuesday next week. Temperatures will drop some 20 degrees from Monday to Tuesday. Several inches of snowfall is possible above 7000 feet. 

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, thunderstorms clouds, chance of thunderstorms slight chance of rain/snow
Temperatures: 55 deg. F. 35 deg. F. 35 deg. F.
Wind direction: SW SW W
Wind speed: 5-10 5-10 5-10
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Friday Friday Night Saturday
Weather: clouds, thunderstorms clouds, chance of rain and snow slight chance of rain and snow
Temperatures: 50 deg. F. 30 deg. F. 52 deg. F.
Wind direction: SW W W
Wind speed: 5-10 5-10 5-10
Expected snowfall: 0 in. 0 in. 0 in.
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