One blue ball was observed.

Condon Report: 1211-B. McChord AFB, Seattle, Wash., 2 October 1959, 0020-0320 LST. Weather: clear, fog moved in at 0150 LST after initial sighting, wind from 100 at 10 knots (approx.). Radar at McChord AFB picked up a total of five or more unidentified tracks between 0020 to 0320 LST. These targets appeared to be at elevation angles of about l0° -20° and azimuths of l70° -l90°. The range would change from 4,000 yd. to 8,000 yd., and the flight patterns were described as "erratic;" returns would occasionally appear in pairs. The radar blips were described as "weak." Data on the vertical beam width and the antenna pattern characteristics of the radar are lacking.

Visual observers were apparently told to go outside and look for an UFO at about 10° elevation and 190° azimuth. They found one - "round," "the size of a quarter" (distance not specified), "white and blue flickering light," a rather good description of a scintillating star. There was a second magnitude star at precisely the correct azimuth (190°) at the time, although the elevation angle would have been only about 1° or so. A sharp temperature inversion, with mist trapped below it, could have easily produced the effect of larger size as well as increased the apparent elevation angle by about 1°. Even trained observers consistently over-estimate the elevation angle of objects near the horizon., as in the "moon illusion" (the apparent increase in size of the rising moon).

When "last seen," at about 0150 LST, the object was reported to be about 20° elevation and 170° azimuth. At that time another bright star (0.7 magnitude fainter than the first one) was located at about 172° azimuth and about 10° elevation, values commensurate with the apparent visual position (again, assuming over-estimate of elevation angle). Near the horizon these were the only two stars of third magnitude or greater in that part of the sky at that time.

The description of the radar targets, weak, erratic blips, together with the reported formation of a low-level fog (that hindered visual observations after 0150 LST), suggests the presence of a shallow temperature inversion-humidity trap that was producing AP echoes on the radar set. The UFO report states that temperature inversions were "prevalent" in the area.

In summary, this UFO incident appears to have been caused by radar AP echoes and associated visual star sightings, both observed at small angles through a surface temperature inversion-humidity trap layer.

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