L.A. Weatherman PRANKED on Live TV -- 'Happy Birthday Hugh Janus'

Someone ripped a page outta the Bart Simpson playbook this week to prank an L.A. weatherman ... asking for a birthday shout-out for "Hugh Janus" ... and it went down PERFECTLY!!!

Ya gotta see this ... KTLA weatherman Henry DiCarlo was giving his usual TV shout-outs for birthdays, anniversaries, etc. ... when he read the name of a supposed 10-year-old boy named "Hugh Janus."

That's when the two anchors LOST IT ... instantly realizing DiCarlo had been pranked and laughing their faces off.

Eventually, one of the anchors let DiCarlo in on the joke ... "I think it was one of those trick names and you fell for it."

Once DiCarlo realized he'd been tricked he admitted, "I got punked" ... adding, "Hopefully there's not a 10-year-old really with that name out there."