My cat is petrified of thunder...?

If he is really botherd by it, you can contact your vet and see if they would be willing to prescribe diazepam. This is animal valium, and it will help calm him down during storms. There is also a medication called clomicalm. This is an herbal supplement that is not a controlled drug that is supposed to work in the same way. I know here in Pennsylvania, I can get clomicalm in pet stores. You definitely need to see the vet for diazepam though.