Genuinely noticed this myself a few times around Herefordshire. Had a spirit box session last autumn during a proper storm and the responses were clearer than anything I'd captured before, which was odd because I'd expected the interference to make it worse.
My working theory, if you can even call it that, is something to do with the electromagnetic charge in the atmosphere. Ley lines maybe? I'm no expert on the science side of things but it feels like theres something to it.
Not convinced its poltergeist activity specifically though. Could just be our brains being more alert during storms, more suggestible, picking up on normal sounds and reading them as something else. I'm always trying to rule that kind of thing out first.
Anyone got actual documented cases or recordings from storm conditions? Would be interested to compare notes rather than just trading anecdotes.