Convergence flying in Central California
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Convergence Flying
Central CA’s Superhighway
Friday, February 21, 14
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Agenda
• Define and debunk
• Characteristics and locations
• How to use it
• Flight log review
• Tools for predicting it.
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Convergence
• What is it?
• Two dissimilar airmass coming together
• Seabreeze convergence
• Two similar airmass coming together
• Techachapi shearline
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Misconceptions• magical smooth line of continuous lift
• vertical line of lift
• There are only thermals in the convergence
• You don’t have to thermal in the convergence
• “the convergence” singular
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Reality
• Often just a line of “better” lift
• meanders about
• tilted
• Thermals are just stronger and larger
• Clouds may only be marked along the line
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Where?• Moves throughout the day.
• Generally along ridgelines and across valleys
• Pushes east throughout the day. Typically.
• Is where you find it.
• Hotter days, farther west.
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How to find it?• Clouds on the obvious days
• Dust Devils
• Surface winds. Will be nearly calm on the ground.
• Use ponds, smoke, haze,dust, tractors, birds, trees or anything you can to identify surface winds.
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Using it• Fly along the convergence line
• Thermals will be aligned and sometimes nearly continuous.
• Speed-to-fly, stop in the best lift only, avoid circling if possible.
• If there are clouds, don’t leave the clouds.
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Blue days• The convergence is often blue RH<50%.
• It’s still there. May only be 200ft across.
• Fly by braille.
• “Drunk” flying
• subtle course corrections back and forth across the line
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Cloud Days• Enjoy the visuals
• Look for shelfs in cloudbase. Fly the higher side.
• Best lift will consistently favor one side of the clouds. Usually the upwind side at alt.
• Jellyfish clouds on the marine side
• Often can get above cloudbase
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Shelf Clouds
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Jellyfish Cloud
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Minimal Thermaling
• 3-29-13
• 418km
• 3:47
• 110kph avg
• 14% of the flight circling
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RASP• Regional Atmospheric Soaring Prediction
• avenal.raspmaps.com
• Run by volunteers for specific areas
• Very high resolution grid 1.3km - 4km
• Able to resolve convergence lines
• Up to 4 days advance notice
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HCrit
• Height of Critical Updraft Strength
• Useful in flatter areas outside of the convergence.
• Generally tells you where thermals top out in a glider ~200fpm or less lift.
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BL Top
• Boundary Layer Top
• Height that thermals will go
• Generally gives a better sense of top of lift in mountains or in the convergence
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BL Max Up/Down
• Convergence predictor
• convergence shows up as yellow, organge, red line
• Very accurate
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Surface Winds
• Useful for guessing at convergence
• General areas of lighter wind
• Stronger thermals
• Slopes that will be likely to work
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Updraft Velocity
• Barely use this one, most of the time the thermals are strong enough
• Buoyancy Shear ratio can be helpful
• Windy days will show if the thermals will be torn up
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850mb Vertical Velocity
• Winds and vertical velocity at 5000ft
• Generally aligns with BL Max Up/Down
• Also shows wave on really windy days.
• 700mb is at ~10,000ft msl
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Live Demo of RASP
• What to look for?
• How to read?
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View Traces in SeeYou
• 3-29-13 - flight with Keith
• Very efficient day. Late start, fast speed.
• 5-12-13 - flight with Martin
• LA Basin and back
• Shows shift in convergence later in day
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Questions/Videos
• ???
Friday, February 21, 14