The bottom of the scale, a white, is the weakest return, and the top of the scale, a pale pink, is the heaviest. One can easily tell how hard it is raining at any given location by looking up the rain rate on the coloured legend. The two most common are higher ground and anomalous propagation . A line of hills, such as the Wentworth Hills, South Mountain in the Annapolis Valley, and parts of the Avalon will show an unmoving return, making it look as if it is always raining there. To detect this, all that is required is to notice that the echoes are always there, regardless of the weather.
Anomalous propagation is caused by the atmospheric structure itself.
Sometimes a line where the atmospheric density or temperature changes very rapidly will cause the signal to be bounced back. Even experienced meteorologists have to study these areas carefully to be certain. It is fairly uncommon, moves erratically and appears and disappears suddenly.