Being afraid of loud thunder is far from bizarre. I believe that humans are born with only 2 ingrained fears...fear of falling and fear of loud noises.
I hate bad storms too. And I do the " Uh-oh, tornado warning !" thing too. I think that as we get older, we watch more t.v. (i.e the news) which in turn has us all watching about the town that just got mowed over by a raging tornado. As kids, we never watched the news, so we really didn't hear of such things. One of those "what you don't know..." kind of things.
If you fear spring/summer weather, you're not alone. There are a bunch of us cowering right along with you.