additive synthesis mebbe. next time theres a storm, just pay attention to the sound from start to finish - youll get an idea of how to emulate it.

listen to Bernard Parmegiani's De Natura Sonorum and La Creation du Monde. there's one track in Natura Sonorum where he creates the sound of thunder using hundreds of lil blips.

done 30+ years ago btw

You would need special speakers to play the real sounds, which go way below 20 Hz. As it says on the NOAA page, the versions they have are pitched up a lot to make them playable on normal equipment. You would not even be able to "hear" the real sounds anyway, they would just shake the room and probably make you feel a bit anxious.

http://en.wikipedia.org/wiki/Infras...s_to_infrasound

malstroem synth in Reason has a thunder waveform
its great. that and rain