Flashes and lightning generated in one pass

The above animation was generated with a 2-level timeline.

The first level animated the lightning, both in strike position and in zig-zaggyness (is that a word?)

The second level of the timeline provided the flashes precisely located at the tip of the strikes.

You could add further levels, too. For instance, to add a sharp background illumination to the whole image, or perhaps most of it, to match the lightning stikes and sparks.