Its a little out of your' way but the Missouri should fish real well in late May and June, river stretch would be Holter-Pelican point North of Helena MT. Tailwater fishery so runoof usually isn't a problem. San Juans, caddis puppa, lightning bugs, and scuds all fish well on that river during that time period.
Brooks Montana Fly Fishing, Missoula Montana, Montana Fly Fishing for Trout. Classic Journey Outfitters.