Anomalous Propagation

Anomalous propagation is a radar phenomenon in which unusual atmospheric conditions — typically a temperature inversion, where a layer of warm air sits above cooler air near the ground — bend the radar beam's normal path, causing it to reflect off the ground, the sea surface, or atmospheric boundaries and return a false "target" that appears on the scope as if it were a genuine solid object in the sky. The effect is a well-understood, extensively documented artifact within radar meteorology generally, entirely independent of ufology, but it carries outsized significance for UFO history because it was the U.S. Air Force's official explanation for part of the celebrated Washington, D.C. flap of July 1952, in which National Airport radar operators tracked mysterious returns that partly coincided with, and partly diverged from, simultaneous eyewitness sightings. The explanation remains genuinely contested rather than settled: temperature-inversion conditions were confirmed present over Washington that week, lending real scientific plausibility to the anomalous-propagation reading, but critics note that not every radar-visual detail from the flap fits the phenomenon's known behavior, particularly cases where the visual and radar reports aligned in ways anomalous propagation alone wouldn't produce. It remains the standing caveat every serious radar-visual case investigation must formally rule out before treating a radar return as evidence.