Doing the weather is often serious stuff, and does not usually lend itself to "April Fools" stunts. (I once worked with a weathercaster who did an entire forecast around a mythical snowstorm coming to Decatur, Illinois. Kinda funny I guess, but he took all his allotted time on the fake snow, leaving no time for the real forecast. Mistake.)
However, I've been involved with a few April Fools stunts that did not compromise the integrity of the product, and were fairly funny.
When I was in radio, I convinced my brother that a local car dealership was having a "buy one, get one free" sale, and I had the inside information because I would be doing the live remote broadcast.
That same year, I also convinced my sister Cindy, (a big Whitney Houston fan at the time) that Whitney was coming to town for a concert, and due to a hotel mixup, Whitney would be staying at my house.
When I was a TV weatherman in Decatur, Illinois, I also did the weather for a local radio station, WLRW. Through much effort, I arranged an "interview" for them with legendary broadcaster Ed McMahon, that happened to fall on April Fools day. I was worried the morning host, a good friend of mine, would be skeptical, but he fell for it. This one was very satisfying for me, because the scheduled "interview" was for 8:40 am, and I got to listen to his entire morning broadcast promoting this "big" interview. He even played the Tonight Show theme in it's entirety every half hour.
Perhaps the stunt that received the most attention was suggested by a co-worker of mine, The "April Fools Day festival." For my entire morning radio show on WSOY-FM, I was broadcasting live from the festival, where we were offering free breakfast, live entertainment, and even an appearance by the great actor Jerry Van Dyke. However, not once did I say WHERE we were broadcasting from.
Many got the gag, but many others didn't. Personally, I thought it was a pretty funny joke, but our receptionist begged to differ, and she stopped speaking to me for a while after that.
I think she was a little sad she didn't get to meet Jerry Van Dyke