The short-wing or "summer" stone on the Yakima is a summer-fall hatch. This is the time of the year when the skwalas and early brown/black stones begin to move around. They are typically smaller and "flatter" then summer stones. Leuctridae? Both can be matched in this phase with olive/brown chenille "Pat's Stone" patterns, BH Prince, the "Girdle Bug" or others.
This particular nymph was crawling around in the snow near a downed log, about 10 yards from water, 1-2 pm, water 37-38 degrees.