Intense lightning three hours after squall line passed

[Pileus]

Have never seen such frequent lightning so far behind a squall line. Squall line passed around midnight in central Carolinas on 4/5/11, and the lightning was still intense at 3am. WeatherTap's lightning detection product was showing strikes 100 miles behind the line. Somebody explain the dynamics for this. Thank you.

[meteorologist]

http://www.spc.noaa.gov/exper/ma_archive/