Winslow, ArizonaFebruary 1963

On February 28, 1963, hundreds of people across Arizona, New Mexico, and California saw an unusual luminous ring-shaped cloud near sunset. The object appeared near Winslow and Flagstaff, Arizona, and remained visible from as far away as Tucson (190 miles south), Albuquerque (to the east), and Los Angeles (to the west). The cloud had a remarkable size of approximately 50 miles in diameter and took on a distinctive oval shape with a clear center, resembling a smoke ring or horseshoe when viewed from different angles.

What made the sighting particularly striking was its extreme altitude and unusual behavior. According to Dr. James E. MacDonald of the University of Arizona's Institute of Atmospheric Physics, the cloud reached a height of approximately 35 kilometers, or about 115,000 feet. This altitude far exceeded the known height limits for ordinary water-based clouds, which typically do not rise above 42 kilometers. The phenomenon remained sunlit for 28 minutes after the sun had already set at ground level, and observers noted beautiful iridescent colors including green, blue, and pinkish hues. Some witnesses described a "wood grain" texture across parts of the formation. The cloud moved generally southeastward during the observation period.

Dr. MacDonald's investigation drew on photogrammetric analysis of four photographs taken in Tucson, as well as weather sounding data from Winslow collected just one hour before the cloud appeared. While he initially considered the possibility of an extremely rare high-altitude nacreous cloud (sometimes called "mother-of-pearl" clouds normally found only in arctic regions), he noted that atmospheric conditions around Flagstaff were not conducive to such formations. The height, latitude, shape, and internal structure all suggested something unprecedented. Requests for additional photographs from sites across Arizona promised to yield better data through triangulation, though some conflict existed between height estimates derived from Tucson photographs and from sunset geometry calculations. The mystery of the cloud's origin remained unresolved, though Dr. McDonald ruled out conventional explanations such as jet aircraft contrails, which could not form at such altitudes given the atmospheric conditions that day.

The origins and nature of this phenomenon remained undetermined, though some observers speculated it might have been a vapor trail from an unidentified high-flying spacecraft. The full case file, containing 36 pages of investigation records, photographs, atmospheric analysis, and correspondence, is reproduced below as held by the National Archives.