Sounds like trophospheric ducting, where vhf and uhf signals propagate
beyond line of sight (do a search on google for tropospheric ducting for
more info that you care to know).

"Antonio" wrote in message
...
Today while driving, I was listening to WDOD 96.5 near Chattanooga,
somehow they were off the air..and instead there was a Mexican station
taking over the signal, very strong signal, fading and coming back,
then there was another Mexican station in the same channel.By the city
and frequency I found it to be XHRN-FM in Veracruz.It was the same on
other frequencies, like 94.5FM, there were 2 or 3 Spanish stations(One
of those was from Mexico City, Insituto Mexicano de la Radio
XHIMER,playing classical music). Then I moved to 101.7 and there were
another 2 spanish stations there.
Why does that happens and how often? I think it has to do with the
weather being hot and humid.
Any comments about that?