[Western Phil]

A small part of the electromagnetic energy radar beam sent from the radar is reflected back by the rotating turbines. The radar processes this "returned energy" as an area of precipitation and plots it accordingly on the map. This contamination of the base reflectivity image as illustrated in the below image, has an effect on the radar algorithms used to estimate rainfall and to detect certain storm characteristics

The interference from the Twin Groves Wind Farm east of Bloomington, Illinois seems to exist only when the blades are wet. Seems as though frost & heavy dew will sometimes cause reflections. There is no way for me to observe if the rotation has an effect, but I suspect it does. There is rain moving past just now (6:50 pm) and the farm is visible as stationary green on Weather Underground animated radar.

[Norman Conquest]

So on clear, dry days the turbines cause no problems. It’s only on stormy days that they’ll create false positive reports of dangerous storm activity? No problemo!