radar shadow[′rā‚där ‚shad·ō]
A region shielded from radar illumination by an intervening reflecting or absorbing medium such as a hill.
ii. A phenomenon in the weather radar when radar energy is unable to penetrate the storm and is attenuated to an extent that there is no return from the storm. A radar shadow can result from an attenuated signal from a nearby storm, masking a larger and more dangerous storm behind. Thin lines of red are often seen connecting two large strong returns and bowing out on the backside. This indicates that a massively powerful thunderstorm may lurk in the black and apparently benign area behind the thin line of red. Radar energy is being attenuated (weakened) so badly that it cannot get back to the receiver to advise the pilot of the real danger. The black area behind the red, showing no return, is called a radar shadow.