Several of these contrails are from B-52 aircraft, which typically fly between 30,000 and 50,000 ft (9,144 – 15,240 m). I often see them and their attendant contrails late in the day heading back to their base in South Dakota. I’ve counted as many as 22 flying at the same time. On this early fall evening, the upper air winds were light so the contrails had been stationary for more than an hour. The profusion of trails and the amount of sky they cover speaks both to the number of jet aircraft streaking across the midsection of the US on any given day and to the availability of moisture aloft on this particular day. Photo taken in September 2006.