Brrrr.
Too cold for me is relative. If I'm acclimated to 80°, 50 might be too cold for me - especially if I can wait a few hours and get 60.
I haven't had to run in anything below freezing for many years, but I've done 35° recently and been fine. I do have to watch my hands though, because I seem to have a touch of Raynaud's.
I'm lucky that I don't have to worry about cold right now, anyway. I did my 11-mile boardwalk loop. I went later in the day than I usually do, so there were a lot of other runners out, which was kind of nice to see. I saw a couple of baby mourning doves on the ground in the park. 
I'm doing the Level II Chi Running workshop this Sunday. So excited!
Speed comes from what you put behind you. - Judi Ketteler