Board Thread:Wiki discussions and announcements/@comment-1990160-20150120053916/@comment-1990160-20150324224837

Some independent users have studied Riot's methodology for free week champions, predicting them with a fair amount of accuracy. However, I believe that user has faded into obscurity, and we do not know for sure which champions will be on the upcoming rotation. There are also little things, like how Yorick is apparently off of the rotation, because Riot supposedly wants players to forget about him until a full rework is imminent.

For an example, please see: https://docs.google.com/spreadsheet/ccc?key=0Arh3w_1KfCECdEl3UUUyZ0pFSFBWcmpaTDVfa1lBUGc#gid=0

The person(s) maintaining the document can use it to predict which champions/skins will likely be in an upcoming sale, but not the exact ones.