These gnats were abundant early in May, but are nearly gone now. I figured I'd try to get a photo before it was too late. I found this specimen perched on a sweetgum leaf in the shade. I managed to get one shot before it flew off, but the shot turned out well.

ID based on recent BugGuide photos from the southeast. (1) (2) In the 100% crop I think I can see the eyes meeting above the antennae as described in Borror & White. (3)