periodical cicadas - four years early??

Cicadas emerged two weeks ago in our neighborhood, littering the ground with their molts.  I'd never before seen them still in their shells, or emerging, so this was  an amazing thing to witness! I've only heard one call so far, but these creatures don't typically emerge until the weather has been stiffling hot for days (last year they emerged in June, the third week of middle summer), so having them appear now, in May, is a little eerie.  Looking back at my posts from a year ago, this is when we found the periodical cicada in Virginia, which is what I think this brood is - not the annual black-eyed dog-day cicadas that we've had here before.  According to brood maps and time tables like this one, these are 17-year cicadas, arrived four years early...