[MENTION=8927]HankAAFlyer[/MENTION] put together a pretty comprehensive list of lounges accessible via Priority Pass or AmEx Platinum at Southwest airports, and how easily accessible they are to Southwest passengers in this thread: http://www.flyertalk.com/forum/south...flying-wn.html (post 9 in the thread has most of it and has recently been updated with 2017 information).

Looks like you might be good if you use EWR and LGA (latter outside security), and IAD