This data come from the Blitzortung lightning detection project, full map can be found here:
http://www.lightningmaps.org

If you would like this as an overlay for GR Level 3, add this to your placefile manager:
http://www.k5ktf.com/sparks/placefile.txt

More placefiles can be found here:
http://www.redteamwx.com/grlevelx.html

Blitzortung Station #1703 Idle (Austin, TX, United States / Texas) - click for details. Station #1734 Offline (Oakhill, United States / Texas) - click for details. Station #1742 Offline (Oakhill2, United States / Texas) - click for details. Station #1743 Offline (Oakhill3, United States / Texas) - click for details. Station #1942 Offline (Cedar Park, TX, United States / Texas) - click for details. Station #2322 Offline (Round Rock, United States / Texas) - click for details.