"Charlie, look at these interesting clouds! What do you think this means? Is the weather going to change or stay the same?"
Charlie: "Why is the weather going to change?"
Me: "Because a big storm is coming."
Charlie: "Thunder can't hurt us, it's just loud noise."
Me: "That's right, but I'm talking about a different kind of storm. This kind of storm is very big, and starts very high in the atmosphere, up where airplanes fly. And this storm is going to make it rain and make the weather very cold afterwards."
Charlie: "Where is the storm coming [from]?"
Me: "It started out over the ocean west of here, do you remember when I showed you west and east on your globe? And then it went to California, and soon it is going to move over Texas and bring us rainy weather."
Charlie: "Why it moves?"
Me: "Up high, verrrry very high above the earth, it is verrrry windy. The wind moves things like storms and airmasses around, which make our weather change."
Charlie: "Why move air-mah-sess around?"
Me: "An airmass is a huge blob of air down at the surface where we live. It can be a cold airmass, like the one that is coming here later this week, or a warm airmass, like the one that is here now."
Charlie: "And the wind WAYYYY up high [indicates 'way up high' with outstretched hands] moves them around?"
Me: "That's right, and that is what makes our weather change."
Charlie: "Plants like the rain."
(And then I changed the subject because Intro to Atmospheric Science was enough for the fifteen minute drive to preschool. Besides, I like to let Labmama handle the biology.)