Changes in barometric pressure and ions before and during electrical storms can affect sensitive dogs.
I hope they get him back and have his ears checked.
He may have some middle/inner ear problems that make thunderstorms especially troublesome for him.
I mean, perhaps I am wrong saying “nerves”. I've suspected that about my old dog.
She was (originally) the opposite of stated here - afraid of gunfire (and anything like it), but not thunder (until she linked it with fireworks; gunfire = fireworks = thunder).
She was scared of guns early - a breeder big into Euro dogs checked her after we bought her, at 3 mos, and declared her a coward and untrustworthy.
Well, he was dead wrong. She was a tough nut who only had a couple Achilles heels, and she NEVER was untrustworthy or even showed she might be.
I suspect sometimes Shana had extremely good hearing.
Meanwhile, my current dog never could’ve cared about gunfire - but she was indeed a coward at the start. Afraid of shadows, bags, etc. She's actually better as I nurtured her, but she is a poor German Shepherd.
I also suspect (not from this but many other things) that Tara has so-so hearing (for a dog).
So now, I really wonder how much is “cowardice” and how much is just “pain”.
Nonetheless, it still isn't good to have a serious working dog afraid of a common occurrence!