Paul Caron has the scoop. Apparently, Northwestern is issuing about 15-25 of these letters every year: The letters tell 1L applicants that they have been turned down for 1L admission but that they will be admitted as transfers if they can achieve a particular GPA or class rank at another school. The goal being, presumably, to get students who they want but who have low numbers that might hurt the school’s US News ranking if they enrolled as 1Ls.