"Right as Rain"

       Standing outside my car I'd just locked, I noticed I hadn't put the the window all the way up.  Since I was in a hurry, I quickly decided I didn't need to unlock and roll--it wasn't going to rain.

       Next day got to the car, smiled and said, "I was right as rain."

       Which surprised and delighted me and led me to wonder the phrase's origin.  Nothing notable I can find, but the frisky, single-syllabled alliteration is catchy.