It reminds me of what I once saw. I was in the car waiting for someone and kind of day dreaming, looking at the clouds. I had my sunglasses on. The sun was in the west shining somewhat through some of the many clouds in the sky. Through one of the clouds off in the distance my eyes focused on a huge form I could plainly see moving through the cloud. It was very huge and long , fairly flat and dark. As it moved through the sunlit cloud, I watched as it should have become more visible coming out of it, but as it should be moving out of the cloud there was nothing at all visibly there. I think that it was a huge flying object that was masking itself, but somehow the combination of the cloud, the sun and maybe my sunglasses served to unmask it.
Saw something like that once without the clouds ... driving up a long hill toward a local small plane airport ... something shinny, gray, huge like a blimp shape stretching from the tree line on one side past the tree line on the other (maybe 50 yards in width) nose was rounded as it slowly crossed the distance. when I got to the top of the hill - a flat area, could see for miles, it was gone - poof - like it never was.
There had been numerous UFO reports in the area at the time all about a huge shape as I recall.