Here are a couple of surface patterns I prefer for this hatch, as one sits right in the film, and the other sits on the film. I like these patterns because the naturals they imitate tend to be slow to leave the surface as they fill their soon to be wide, blue-gray wings with life giving fluid in the cool, spring air.
This first one is a simple soft-hackle, size 20. Tail is a few fibers from a dark, mottled Hungarian partridge neck feather; the body is dark olive with a touch of brown; and the hackle is also a Hun neck feather. I fish this fly just as I would a dry.
This one is a no-hackle, also tied on a size 20 hook. The tail is a few Hun neck feather fibers; the body and thorax again is dark olive; and the wings are primary feather sections from a mallard wing. Those wings stay together as they are here for about all of two or three casts, then they generally splay in place and the works great.
Tie some up and fish them!!!
And don't forget to sharpen your hooks.