needing mommy advice

My oldest son J is 5 1/2  is obsessed with tornados. At first it seemed like it was more of an interest and fascination but now it seems like it is turning into a FEAR. He has woken up in the middle of the night saying he had a tornado dream. He has imagined them outside his bedroom window on the calmest of nights. We just don't know what to do with him about it. We have told him to pray when he is afraid and God will help him through it. We have prayed with him before he even goes to sleep. We let him know that we have a storm radio that alerts us if a storm is coming so we can get into the basement in time. Nothing seems to help. Please if you can think of anything that we haven't tried or if you have dealt with a simular situation let me know.