The rain can help improve the fishing quite a bit, especially in clear water.  The thunderstorms can definitely spook the fish for a day or two, but this isn’t always the case.  The severity of the storm definitely plays a role in how the fish react afterwards.  A bad thunderstorm followed by a cold front creates the worst situation for catching bass.  Bass can be inactive up to 3 full days after these situations.  Some fish can still be caught, but it is a lot tougher during these conditions.