Take a look at this cool time-lapse video:
taken last year in Tama, Iowa from KCCI-TV's (Des Moines) tower camera there.What you are looking at is a gravity wave. The physics is quite complex, but in a nutshell, they are waves caused by changes in air flow.
It can either be caused by topography, such as air flowing over mountains, or by other dynamics, such as the turbulence created by a generating storm front.
Here is a photo gallery of another event of gravity waves over Iowa, this one in 2006 by KCRG-TV is Cedar Rapids.