Convergence flying in Central California

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Information about Convergence flying in Central California

Published on February 21, 2014

Author: morhall



A talk I gave to the San Luis Obispo Soaring Association on flying the convergence line in central California. This is from the perspective of a sailplane pilot, but applies to Hang Gliders and Paragliders as well.

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 • • 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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