Cumulonimbus

When Calvin was little, he loved Little Einsteins.  Quincy, Leo, Annie, June, and Rocket were his favs!  Fortunately, we didn't find them too annoying because he really learned a lot from those videos.  One day when we were taking the girls to school

he points to the sky and shouts (with great articulation...if you were around him at that age, you remember how in awe we always were with the things he would say) "CUMULONIMBUS!"  Makes me smile as I hear his little voice in my head every time we have thunderstorms.  And it's been a lot lately.  Why do they have to grow?