On NW, the F bucket is the upgradeable bucket. P (Premium) is paid first class.

I'd say you have a pretty good chance for an upgrade as rev. management may either move some P seats over to the F bucket or as P seats go unclaimed day of departure. Be sure to check in online 30 hours before the flight to get waitlisted (although you will be waitlisted automatically during EUA). If nothing else, it is a short flight and try get seated in 6D, row 5, or the exit rows 14 or 15 (I am assuming this is a DC 9-50). On an empty flight you may find that those coach seats are actually more comfortable than F provided that no one else is sitting next to you.