When we were at the mountain house for the 4th of July, TJ had Adam outside during the beginning of a storm. I went out and asked him to bring Adam inside, and TJ basically ignored me. 2 minutes later, the loudest clap of thunder ever sounded, and poor Adam freaked out.
Two weeks later, we were home and TJ had Adam outside once again. A storm started brewing, and yet again, TJ kept him out too long, and KABOOM! huge thunderclap and trauma inflicted upon our youngest child.
Ever since, Adam will hear any sound (airplane, car, etc) and get a freaked out look on his face and say, "Thunder! Thunder!" (okay, it sounds more like "Thundah! Thundah!") Sometimes he will add "storm" to it too.
So today we were hanging out in the playroom, it is bright and sunny outside, and Adam runs into the puppet theater saying "Safe! Safe! Thundah storm!" Apparently, he now has a safe place to stay.