When sulphurs are emerging, a CDC wing emerger pattern is a good bet:
Another pattern that is good to use if the trout are taking emergers is a biot bodied sparkle dun. The hairwing allows for good flotation especially in slow moving waters, and is reasonably visible from a distance.Sometimes the trout target the duns, and when this is the case a CDC comparadun is a very good choice. The CDC wing is easily visible and floats very well. Treating the wings with a floatant allows the wing to stay above water, but the body floats flush with surface.
Finally, the last stage of importance during a sulphur hatch is the spinner fall. Only once have I fished a spinner fall, and I was completely unprepared. Now, I have developed this spinner pattern. The body color is actually tan since the spinners of E. Invaria and E. Dorothea commonly turn a tan color before falling spent on the surface. I do not have a picture of this pattern, but there are pleny of them floating around on the internet.
Sulphurs are a key food source for trout in the late spring in the Tennessee Valley. Understanding the differences between the two species of sulphurs present on East Tennessee tailwaters, and the flies that best imitate each phase of the emergence will be a good start in finding success during this very common late spring event.