The ranking of the waitlist is somewhat rolling (the score an applicant gets during the admissions process is how they're ranked...above 6 or 6.5 (can't remember exact score cutoff) is acceptance, below 5.5 is rejected, 5.5-6 is held until March or April when the remaining acceptances are given and everyone else between 5.5 and the cutoff score is waitlisted. So some years 5.5s will get in and other years they may only get to 5.9 or 5.8s by waitlist movement). I'm guessing on the score cutoffs, but the concept is correct.
This info is available via links from the LCME link from the med school homepage. FYI, UW will not tell you your score ("confidential"), just your # on the waitlist.