My nephew & I have figured it out about flash ending up on Supergirl(based on watching sneak peeks of the Supergirl episode on You tube). Based on one of the sneak peeks, Barry/Flash has this strange looking metallic circle thing around his emblem. My nephew said that it looks like something that Eobard Thawne/Reverse Flash would wear, & we know that the Flash is going back into time Tuesday to actually get help from "Dr. Harrison Wells" Eobard Thawne to become faster. Well, I'm guessing that it works & Barry travels back in time 24hrs from Tuesday tomorrow night to Monday Tonight on Supergirl. So maybe in reality, tonight's Supergirl episode should have occurred next week instead of tonight chronologically speaking.