Riders on the Storm

I've got to share these pictures I took on the way home one night last week (I think it was Thursday).

First of all, this is what the sky looked like when I left work. Pretty amazing.

(click for wallpaper size)

But then, driving into Madison, things got weird. Look at this wall of clouds it looked like I was driving into. I've never seen anything like it. I didn't get any real good pictures driving beneath it while I was in Madison. It appeared to be a group of fast moving clouds (going south, maybe?) that were only about 20 or 30 feet above the ground. Bizarre.

Then I ran into a similar phenomenon driving into Athens, though, by this time, it was much darker. It looks like the evil clouds are reaching down from the heavens.

In that last picture, you can see what appears to be another wall of clouds off in the distance. What's going on here?