As we saw earlier, anomalous propagation (superrefraction) most commonly occurs when sharp inversions in the lower troposphere bend radar beams downward as they travel away from the radar. This phenomenon may cause a widespread cluttered appearance at the ground, or only certain features, such as local hilltops or buildings, may be intercepted. This image shows an example of anomalous propagation.

Here are a few key points to keep in mind about anomalous propagation echoes:

• When viewed as a time series, echoes will not change much over several frames. Some echoes may disappear or reappear, but will do so in mostly the same location.
• The targets' velocities in the suspected area will be at or nearly zero.
• Reflectivity values in areas of anomalous propagation are often erratic and do not resemble any usual precipitation patterns.
• Echoes may also be relatively weak and extend for great distances in a beamlike shape.
• Look at another nearby radar to help determine whether an echo is from precipitation.
• Look at recent satellite data to see if there are actually any clouds present.
• Look at the most recent local sounding to see if a sharp inversion is present.
• Look at a map of local topography to see if echoes are collocated with higher terrain.