Was just about to post this to Facebook and thought "NO, fool! Put it on the blog instead. Bring back that habit!" This is SO cool. Yes, I can smell rain a'coming, and have all my life. (Out where I live, I can see, smell, feel weather all the time and that's a good thing. A necessary thing.)
But I had no idea the reason was so complex (although, doh, of course it would be!). I just figured it was the rise in humidity.
Anyway, this explanation from Scientific American is marvelous and fascinating. Enjoy!