Hind femur pattern seems a bit different, and I would think it would still have the two lines through the eyes that young nymphs have. I usually think of keeleri as a very late summer to fall species in the northeast. I was just starting to find tiny M. keeleri nymphs in NY at around the same time this one became an adult, and those didn't become adults until August! Unfortunately I never got to revisit this spot to check out the males

Once again, thanks for blasting through a bunch of these unidentified hopper photos here in recent days. I went through and looked at all the images you ID'd - really helps me to learn too!