"It's no secret that we have been looking to bring a new goalkeeper in to provide competition," Forest manager Billy Davies told the club's official website.
"Iain Turner fits the bill perfectly. He is a goalkeeper with a good pedigree and great potential and it's a situation that helps both ourselves and Everton."
Turner added: "I'm looking forward to it immensely - it's a great opportunity for me and I intend to grasp it with both hands.
"Forest's league position doesn't concern me. I've played in the Championship before and know how tight a league it is and how quickly things can turn around."