Today (8/3) in eastern Pennsylvania, I saw a white and black bird flying far above. It seemed to be about crow sized. It did not seem to have a very extended head, was all white including the whole wings but had black, sort of rectangular tail feathers. Its wings seemed not to be too big, extending out fairly straight from its body (I think). My first thought was that it might be some kind of gull, but I couldn’t find an all-white gull with black tail feathers from underneath. I did not get to see any of the coloration on its back.
Edit: if you don’t have any luck finding it, try drawing a sketch of it and posting that as an observation. Drawings can’t get Research Grade, as far as I know, but that would help someone potentially ID it for you.