From the FAA AIM(Airman’s Information Manual)
The bending of radar pulses, often called anomalous propagation or ducting, may cause many extraneous blips to appear on the radar operator’s display if the beam has been bent toward the ground or may decrease the detection range if the wave is bent upward. It is difficult to solve the effects of anomalous propagation, but using beacon radar and electronically eliminating stationary and slow moving targets by a method called moving target indicator (MTI) usually negate the problem.
Radar energy that strikes dense objects will be reflected and displayed on the operator’s scope thereby blocking out aircraft at the same range and greatly weakening or completely eliminating the display of targets at a greater range. Again, radar beacon and MTI are very effectively used to combat ground clutter and weather phenomena, and a method of circularly polarizing the radar beam will eliminate some weather returns. A negative characteristic of MTI is that an aircraft flying a speed that coincides with the canceling signal of the MTI (tangential or “blind” speed) may not be displayed to the radar controller.
re: “The bending of radar pulses, often called anomalous propagation or ducting, ...”
This effect can EASILY be seen on weather RADAR in the evening, usually; as disk proceeds, ‘ground clutter’ appears out to a distance of 40 or so miles.
Sometimes, given a warm or cold front passage the ‘returns’ from ground/building clutter becomes much more pronounced, so, those factors should be considered for this event too.