Since selectors can target lightning bolts, they get saved to chunks.
If you use this command setup for a while, and then shut it down and load some chunks, lightning will load in in the newly loaded chunks, looking very odd with the constant flashing of the sky.

summon minecraft:area_effect_cloud ~ ~ ~ {Tags:["lightning"],Duration:1}
spreadplayers ~ ~ 1 300 false @e[tag=lightning,type=minecraft:area_effect_cloud,limit=1]
execute at @e[tag=lightning,type=minecraft:area_effect_cloud,limit=1] run summon minecraft:lightning_bolt ~ ~ ~

Do note, that this setup is only a way to trigger it on demand; it can happen with natural lightning strikes too, just much more hard to do so.