Ormerod has found himself down the pecking order after breaking his leg in January 2006 limited his chances at Preston.
The striker has scored just once in 20 appearances for the Lilywhites this season.
Preston manager Alan Irvine told BBC Radio Lancashire: "Brett's going to join Nottingham Forest on-loan until the end of the season, but with a 24-hour recall after the first 28 days.
"Brett has been frustrated about a lack of opportunities in the first-team and I sympathise with him because he's a great lad and a terrific professional."