Stop scrolling and watch the heck out of this 30 second clip of a lightning strike
This is a film of a lightning strike, caught at over 7200 fps. The entire 30 second film doesn’t amount to a tenth of a second in real time. And the video itself is mind blowing.
Randall Munroe of XKCD has the best explanation:
Tom’s video gives an idea of how lightning moves. It starts with a branching bundle of charge—the “leader”—descending from the cloud. This is what you see in the first part of the video. It spreads downward at speeds of tens to hundreds of kilometers per second, covering the few kilometers to the ground in a few dozen milliseconds.
The leader carries comparatively little current—on the order of 200 amps. That’s still enough to kill you, but it’s nothing compared to what happens next. Once the leader makes contact with the ground, the cloud and the ground equalize with a massive discharge of more like 20,000 amps. This is the blinding flash you see. It races back up the channel at a significant fraction of the speed of light, covering the distance in under a millisecond—all within a single frame of that video.
(Technical detail: while it’s called a “return stroke”, charge is still flowing downward. However, the discharge appears to propagate upward. This effect similar to how when a traffic light turns green…, the cars in front start moving, then the cars in back, so the movement appears to spread backward.)
So the place on the ground where we see a bolt “strike” is the spot where the leader first makes contact with the surface. The leader moves down through the air in little jumps. It’s ultimately feeling its way toward the (usually) positive charge in the ground. However, it only “feels” charges within a few tens of meters of the tip. If there’s something connected to the ground within that distance, the bolt will jump to it. Otherwise, it jumps out in a semi-random direction and repeats the process.
By the way, if you have any unanswered questions about lightning strikes, definitely jump over to the entire post at XKCD: What if?