On one of my recent rides
I had a following wind on the way back. The road was straight and flat and I noticed that although it was one of those beautiful days when the sky is in motion and all seems right with the world, I always seemed to be in the shadow of a cloud overhead. Then I realized that I and the cloud were traveling South at approximately the same speed (18 mph). I speeded up a bit and started to reach the forward edge of the shadow. Slacked off and that edge moved ahead somewhat. Never experienced that before.