<p>Look at the unweighted.
Assuming that the transcript has a substantial number of APs, and that it is generally the toughest curriculum offered where there are no APs, being well north of 3.7 is key (unless there is some other extraordinary quality, not being assumed here).
And frankly, a 3.7 would just make you competitive, but it would not impress. To impress, I would think being north of a 3.8 unweighted.
Northwestern gets a very strong applicant pool, and getting in is going to get even harder given that the number of applications have taken huge jumps two years in a row.</p>