Intracloud lightning on sunny days

I was once flying underneath a cumulus cloud on a nice, sunny day near Orlando, Florida. The clouds were not unusually tall, and there were no storms anywhere within hundreds of miles, at least. I heard lightning above my head twice; I remember the sound from a large Van de Graaf generator which I’ve seen (& heard) hundreds of times at the Museum of Science in Boston, MA. I later observed a bolt of lightning in another cloud, going between one part of the cloud to another.

I’ve never heard of lightning on sunny days before then, and I haven’t seen it since. I’ve talked to pilots with many years of experience who have never heard of it. How common is this? It is more common in some parts of the world than others?

All cumulus clouds have the potential to have lightning in them, whether or not they’re actually thunderstorming on anybody at the moment. It depends on how high their tops are.

NASA knows all about cumulus clouds and lightning.

http://liftoff.msfc.nasa.gov/academy/rocket_sci/launch/commit/cloud.html

http://www.aero.org/publications/crosslink/summer2001/05_sidebar6.html