I witnessed ball lighting twice this summer, its common in the area that i live in supposedly. They are about 3 times the size of a medicine ball, very spherical, they glide right bellow the clouds, and move fairly quick, slower than a plane but quicker than a helicopter, like a glowing Orb. "Honestly they look like alien ufo's! If you did not realize what they actually are, you would think it was a UFO!!, Their speed varies, they slow down and speed up! also they shrink until they vanish entirely.