Champion's weather duties at ABC will be taken over by Ginger Zee.
"He will become the on-air face of [The Weather Channel], appearing as a host and serving as managing editor. Sam calls it a once-in-a-lifetime opportunity," Sherwood said in a letter to ABC News staffers.
"For 25 years, Sam has been a vital member of the ABC News family -- joining powerhouse station WABC in 1988 and 'Good Morning America' in 2006," Sherwood said.
"Over the years at 'GMA,' Sam has broadcast more than 1,800 weather forecasts. He has traveled to almost every major weather event in the U.S. As many of you know, Sam's 'go' bag is always ready and his stellar reporting during Superstorm Sandy contributed to ABC's Peabody Award for coverage of that historic storm. ...
"While there is no replacing Sam, we are in excellent hands with his storm-chasing partner of the last few years, meteorologist Ginger Zee, who will take over his weather responsibilities at 'GMA' and across ABC News. As you know, Ginger always rushes straight toward the eye of any storm and weaves cutting-edge science with human emotion to elevate our coverage. 'GMA' will celebrate Sam's last day on Wednesday's program. While he is leaving ABC News, he will always be a part of our family."