convergence flying in central california

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.


Convergence

• What is it?

• Two dissimilar airmass coming together

• Seabreeze convergence

• Two similar airmass coming together

• Techachapi shearline


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


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


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.


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.


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.


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


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


Shelf Clouds


Jellyfish Cloud


Minimal Thermaling

• 3-29-13

• 418km

• 3:47

• 110kph avg

• 14% of the flight circling


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


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.


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


BL Max Up/Down

• Convergence predictor

• convergence shows up as yellow, organge, red line

• Very accurate


Surface Winds

• Useful for guessing at convergence

• General areas of lighter wind

• Stronger thermals

• Slopes that will be likely to work


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


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


Live Demo of RASP

• What to look for?

• How to read?


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


http://www.onlinecontest.org/olc-2.0/gliding/flightinfo.html?dsId=2853003




Questions/Videos

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convergence flying in central california

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