Published on February 21, 2014
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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