convergence flying in central california
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Convergence Flying
Central CA’s Superhighway
Friday, February 21, 14
Agenda
• Define and debunk
• Characteristics and locations
• How to use it
• Flight log review
• Tools for predicting it.
Friday, February 21, 14
Convergence
• What is it?
• Two dissimilar airmass coming together
• Seabreeze convergence
• Two similar airmass coming together
• Techachapi shearline
Friday, February 21, 14
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
Friday, February 21, 14
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
Friday, February 21, 14
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.
Friday, February 21, 14
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.
Friday, February 21, 14
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.
Friday, February 21, 14
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
Friday, February 21, 14
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
Friday, February 21, 14
Shelf Clouds
Friday, February 21, 14
Jellyfish Cloud
Friday, February 21, 14
Minimal Thermaling
• 3-29-13
• 418km
• 3:47
• 110kph avg
• 14% of the flight circling
Friday, February 21, 14
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
Friday, February 21, 14
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.
Friday, February 21, 14
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
Friday, February 21, 14
BL Max Up/Down
• Convergence predictor
• convergence shows up as yellow, organge, red line
• Very accurate
Friday, February 21, 14
Surface Winds
• Useful for guessing at convergence
• General areas of lighter wind
• Stronger thermals
• Slopes that will be likely to work
Friday, February 21, 14
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
Friday, February 21, 14
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
Friday, February 21, 14
Live Demo of RASP
• What to look for?
• How to read?
Friday, February 21, 14
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
Friday, February 21, 14
Questions/Videos
• ???
Friday, February 21, 14
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