http://www.museumofhoaxes.com/
Number 9 in the following link, the second half. I remember it very well. Hilarious.
There were also fines.
http://www.museumofhoaxes.com/worstaprilfools.html
In the same genre of non-funny disaster warnings, there's also WNOR's 1992 April 1st report in which it warned that a large build-up of methane gas was about to cause a fiery explosion at Mount Trashmore, a landfill near Virginia Beach. Residents were warned to evacuate the area, causing the local 911 to be flooded with calls. The DJs responsible for the prank were suspended without pay for two weeks.