When the Light Cahill hatch is heavy and many nymphs are coming to the surface, a good technique is to fish a Light Cahill Dry size 14 or Murray's Yellow Drake size 14 on a 5X leader with a Mr. Rapidan Soft Hackle (Brown) Nymph size 14 on a 24 inch 5X mono dropper below it. Usually I catch an equal number of trout on each fly. Don't overlook the Little Yellow Stoneflies. I have seem more of these on the streams this year than I have in the last couple of years. The picture above shows the natural Little Yellow Stonefly. I match this with the Murray's Little Yellow Stonefly Dry and the Murray's Little Yellow Stonefly Nymph.
All of the native brook trout streams in the Shenandoah National Park are in excellent shape. The stream levels will start to drop if we do not get some rain soon. For more information on these streams, see my book Trout Fishing in the Shenandoah National Park.