My last dog actually liked storms and fireworks and thought normal behavior in a storm was to go outside and look up (because that is what Jeff and I do), so when I got Huey, I was determined that he would like storms, too. Dh & I LOVE LOVE LOVE big hairy thunderstorms withs lots of lightening, so from the day we got the Hughster, every time it stormed outside, out we went. We walked around in the lightning and wind and told Huey how much fun it was and how pretty it was, so he had never had an issue with storms. This appears to have carried over to car washes, too, because he has ridden through several with absolutely no change in demeanor whatsoever, like he doesn't even hear it, except he stands up in his carrier to watch the water hit the car.
I don't know if this info will help with an adult dog, but I strongly feel that the dog senses what you feel, and if human is scared of storms, dog will be doubly so. I highly recommend desensitation as a tiny puppy, but I think it will only work if human also loves (or at least is not nervous during) storms. Them something mundane as a car wash? Hey, no problem!
