Almost certainly fake. With the first strike, if you pause when it is at its brightest, the shadow cast by the car closest to the camera wouldn't exist where it does. Basically, the flash is light entirely from a source behind the camera.
Edit: well the shadow is always there, rather the huge amount of light from the lightning should have very much illuminated where the shadow was, but it didn't. Rather the shadow is just as strong as it ever was. That, the way the trees are light up also indicated the source of the flash is behind the camera
Even more edit: Actually, I don't think there was any flash at all, it was entirely done by increasing the levels on the image.