I have never seen clouds like these. The news station’s site says this phenomenon has no name, which is interesting, because although they are rare in Iowa (where these shots were taken), they also say the clouds are more common near mountains.
There is video of the clouds on that site too, and they look like ocean waves, except the waves are under the clouds. I wonder if they are caused by air blowing over hills and setting up a standing wave, a kind of permanent rolling wave. As the cloud blows over, the air would push the cloud up and down, setting up that wave.
But I have no real idea; that’s just a guess. I’ve emailed meteorologist friend but have not heard back from her yet. No doubt someone who reads this is a meteorologist, too, so pipe up in the comments if you know about these things!’