Cassie, our dalmatian, barks and barks at thunderstorms and has all of her life...I don't know why. She gets over it pretty quickly, though. I think the thunder hurts her ears....Was your dog ever in a thunderstorm, maybe outside or something? My sister's sweet dog, Kiska, was in their house when a tornado came through. It blew out some windows, and blew the fence away. She was never,ever the same after. They tried everything to help her, but she never got over it.