It’s like a spark plug in an internal combustion engine (ICE). The voltage gets high enough and manages to jump the gap to the closest conductor. With the ICE the designers and engineers have managed to control that discharge to get optimum performance in a controlled condition.
Weather is a bit different in that we can’t control it like and we can in an a controlled environment like an ICE. Stil, the physics of the discharge are the same.
And yes, lightning will discharge from cloud to cloud.
Good clip.
Even more interesting was this one on the same page showing ‘upward lightning’ - lightning that travels from the ground up to the clouds! According to the video (from Raging Planet), the mechanism for this phenomenon is not understood.
You know it is really the same as how photons “know” to bounce off a mirror in such a way that the angle of incidence is the same as the angle of reflection. One answer is that they try all paths, but end up on the one at which nearby paths do not lead to destructive interference. You can call it the principle of least (more accurately stationary) action, but that is the physical explanation. I assume that the lightening “tries” all paths until it finds one that works. Once the path is found and the air ionized, the resistance drops and the bolt strikes. Fixing a lot of nitrogen along the way, BTW.
Saw this GIF today which should explain it pretty well… a group of streamers spreads out and the first one to ground itself is where the lightning “strikes.”
High-Speed Shot of Lightning Strike
Edit: All too late I see that AaronX has beaten me to the punch with the same footage. And I thought I was being all super-helpful. Shucks.
This video is pretty good. It explains and shows how when the lightning gets near the ground, the ground builds up an opposite charge and sends up streamers. The lightning connects to one of those and rides it’s path to the ground, as had been mentioned upthread. So really, lightning doesn’t know where to place the final stroke, the ground guides it in.
How does the ground “pick” the spot? Why do the streamers go up instead of sideways? When the ground builds up a charge, where’s it more likely to send that charge from, a flat road or something conductive sticking up in the air? The answer is obviously the latter. The streamers are more likely to go up into neutral air than to go sideways and follow along the charged ground. The streamers are essentially trying to get away from that charge, so they go up.
So lightning doesn’t really care about the shortest path to the ground, it’s just that there are conductive things that are not only sticking up that are the first thing lightning encounters on the way down, but they are also sending out a tall electric charge on top of that which attracts lightning because that’s the best spot for it to hit and dissipate it’s charge.
My question has always been, why does lightning miss so much? It often hits the ground near a pole instead of hitting the pole. I’ve never really figured that one out.
