Sooo. . . I would really like to have dinner at Tomorrowland Terrace.
Is there someplace where Disney tells me what "seasonally" means? When are they open and when are they closed?
Seasonally can mean anything from "Rarely, if ever open" (Sounds Dangerous, if that's even there anymore?) to "Open all the time" (Carousel of Progress).
In 99% of the cases though, it means open only during high crowd times.
It was reported open a lot in the May-July period; I think it was open over Memorial Day and am absolutely certain it was open in early July. If you are going during a high-crowd time, it will probably be open, otherwise, probably not.