You probably have experienced tropospheric ducting. This happens usually in a high pressure zone when the radio signal travels in a tunnel of inverted temperature layers in out atmosphere. This occurs in the VHF and UHF radio bands, and you can experience the same thing with television stations.
I have reached over 1500 miles in a short conversation on the 147.200 Mhz Amatuer radio band, which is just a little higher in frequency than your Broadcast FM radio stations. This was from Michigan to Miami, FL!
Other strange radio behavior occurs during meteor showers and high sunspot activity.
Here is a link for more info.
[Link: northcountrypublicradio.org]