did happen a few times in the mid west during the cold war
I seem to remember that the code word for nuclear armaggedon was
'hatefulness hatefulness' - are you listening divebuddy ?
and low and behold if you goggle it, you get
Maybe it was test that was being trialled behind the scenes and was broadcast by mistake. In certain parts of the US, you regularly see test transmissions on TV to warn of trouble (usually weather related)