From the “you learn something new everyday” saying, these are undulatus clouds. Also known as wave clouds or billow clouds, these clouds appear in sheets, patches, or layers, and have undulations that resemble “waves” or “ripples” in water. They are caused by atmospheric gravity waves, which typically form when something forces a mass of air upward. The air the cools as it rises and, if there is enough a moisture, the water condenses and forms clouds. Taken at the George V. Vanderbilt Town Park in Greenville, NY.
Amazing pic