The radar image of the midwest provided by [Weatherunderground](http://www.wunderground.com/cgi-bin/findweather/getForecast?brand=wxmap&query=40.10669,-88.21381&lat=40.10669&lon=-88.21381&zoom=6&type=ter&units=english&wxsn=0&rad=1&rad.num=1&rad.spd=25&rad.opa=70&rad.stm=1&rad.type=N0R&rad.type2=&rad.smo=1&rad.mrg=0&sat=0&cams=0&svr=0&tor=0) at 10:30 PM Central time, May 8 2011 has odd patterns. 

Are these patterns real? Perhaps caused by large scale convection over cities? Or are they artifacts of radar placement?

Here is the image that I am referring to, where green indicates light and yellow moderate rain:
![enter image description here](https://i.stack.imgur.com/xlvW8.png)